Distribution optical elements and compound collecting lenses for broadcast optical interconnect

ABSTRACT

Methods and apparatus are described for distribution optical elements and compound collector lenses for a broadcast interconnect. An apparatus includes a broadcast optical interconnect including: a plurality of nodes positioned to define a node array, each of the plurality of nodes having at least one optical signal emitter and a plurality of optical signal receivers positioned to define a receiver array that substantially corresponds to the node array; and a plurality of optics optically coupled to the array of nodes, the plurality of optics positioned to define an optics array that substantially corresponds to the node array and the receiver array, each of the plurality of optics including at least one optical distributing element and an optical collecting element, wherein an optical signal from the optical signal emitter is fanned-out by the at least one optical distributing element of one of the optics and broadcast to one of the plurality of receivers of all of the plurality of nodes by the optical collecting element of all of the plurality of optics.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims a benefit of priority under 35 U.S.C. 119(e)from provisional U.S. patent application Ser. No. 60/813,970, filed Jun.14, 2006 and is also a continuation-in-part of, and claims a benefit ofpriority under 35 U.S.C. 120 from copending utility patent applicationU.S. Ser. No. 11/796,133 filed Apr. 25, 2007, which in-turn is acontinuation-in-part of, and claims a benefit of priority under 35U.S.C. 120 from copending utility U.S. patent application Ser. No.10/702,227 filed Nov. 5, 2003 (now U.S. Pat. No. 7,450,857, issued Nov.11, 2008), which in-turn claims a benefit of priority under 35 U.S.C.119(e) from both provisional U.S. patent application Ser. No.60/423,939, filed Nov. 5, 2002 and provisional U.S. patent applicationSer. No. 60/432,141, filed Dec. 10, 2002, the entire contents of all ofwhich are hereby expressly incorporated herein by reference for allpurposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of optical interconnectsfor computer systems and/or their subsystems as well as networks and/ortheir subsystems. More particularly, the invention relates to afree-space optical interconnect that includes a fan-out and broadcastsignal link.

2. Discussion of the Related Art

The concept of parallel-distributed processing (PDP), which is thetheory and practice of massively parallel processing machines, predatesthe first supercomputers of the 1960s. In practice, high-performanceparallel-distributed processing machines are difficult to achieve forseveral interrelated reasons. On the physical side of the equation,interconnections between n processors or nodes increase as the square ofthe number of processors (n²); the physical bulk increases as n for thepackaging and n² for the interconnecting wiring; latency due tocapacitance increases as the average distance between nodes, which isalso proportional to n; heat-removal difficulty increases as the squareroot of the number of processors (n^(1/2)) due to the surface-to-volumeratio. On the logical side of the equation, message overhead is constantfor broadcast mode and can increase as n for relay mode. The impact onsoftware is roughly proportional to n² due to the increased complexityof parallel-distributed processing algorithms. The overall cost per nodeincreases more rapidly than the number of nodes when all these factorsare considered. What is needed is a method of parallel-distributedprocessing, design and operation that overcomes some or all of thesescaling problems.

The present record holder in performance is NEC's “Earth Simulator”topping out at 35.86 teraflops (a teraflop is 1000 gigaflops and a flopis a floating-point operation while “flops” usually refers to a flop persecond). While there are many interesting and novel entries in today'ssupercomputer marathon, the Department of Energy's Advanced Simulationand Computing Initiative (ASCI) has sponsored several of the topcontenders. The latest of these is a fifth-generation ASCI system to bebuilt by IBM. The ASCI Purple (AP), if on time and within budget, willarrive by 2005 at a projected cost of approximately $550 per gigaflopwith an ultimate option to have a 100-teraflops performance figure in asingle machine. (A gigaflop is one billion operations per second.) Thisis about 12 times the performance of the previous ASCI Q and ASCI Whitemachines. By contrast, a present-day personal computer is typicallypriced about $750/GF (the minimum cost is probably about $500/GF, i.e.,actually less than the ASCI Purple.) This clearly shows that economiesof scale are nonexistent to marginal given the factor of nearly 13,000increase in the number of processors required to achieve the 100teraflop (TF) figure. (A teraflop is 1000 gigaflops.) The ASCI Purple(AP) is estimated to weight in at 197 tons and cover an area of twobasketball courts (volume not specified). The AP will have 12,433 Power5microprocessors, a total memory bandwidth of 156,000 GBs (gigabytes perseconds), and approximately 50 terabytes (million megabytes) of memory.Power dissipation will be between 4 and 8 MW (megawatts), countingmemory, storage, routing hardware and processors.

IBM's Blue Gene3/L (BGL), based on that company's system-on-chip (SOC)technology, will take up four times less space and consume about 5 timesless power, it is expected to perform at the 300 to 400 teraflops level.The cost per gigaflop will be about the same at about $600/GF as above.Each of the 65,000 nodes in the BGL will contain two Power PCs, fourfloating-point units, 8 Mbytes of embedded DRAM, a memory controller,support for gigabit Ethernet, and three interconnect modules. The totalnumber of transistors is expected to be around 5 million, making for alarge, expensive, and relatively power-hungry node. The interconnecttopology is that of a torus, where each node directly connects to sixneighbors. For synchronizing all nodes in the system, hardware called a“broadcast tree” is necessary. Establishing broadcast mode to begin acomputation, for example, will require several microseconds. To roundout the hardware complement of a node, nine memory chips with connectors(for a total of 256 Mbytes) are foreseen. Four nodes will be placed on a4 by 2-inch printed-circuit card.

Reliability in these existing machines is a major concern when there arefrom hundreds-of-thousands to millions of material interconnections(e.g., wires, connectors, solder joints, contact bonding). What isneeded is an approach to super computer design that increasesreliability.

Moreover, the main, unsolved problem facing today's supercomputers ishow to achieve the economies of scale found elsewhere in the industrialworld. Machines with tens of thousands of processors cost as much pergigaflop as commodity PCs having only a single processor. Part of thereason for this lack of progress in supercomputer scaling is that theinterconnect problem has not yet found a satisfactory solution. Adoptingpresent solutions leads to a reliance on slow and bulky, off-chiphardware to carry the message traffic between processors. A relatedproblem is that communication delays increase as the number of nodesincreases, meaning that the law of diminishing returns soon sets in.This issue drives the industry to faster and faster processing nodes tocompensate for the communications bottleneck. However, using faster andmore powerful nodes increases both the cost per node and the overallpower consumption. Smaller, slower, and smarter processors could beeffectively used if the communications problem were to be solved in amore reasonable fashion.

Broadcasting is an essential feature of parallel computer interconnects.It is used for synchronization, and is intrinsic to many types ofcalculations and applications, including memory system coherency controland virtual memory. Many applications running on today's supercomputerswere written decades ago for relatively small parallel computers thathad good bandwidth for broadcasting. These programs run poorly ontoday's massively parallel machines. The commonly used interconnectsbased on cross bars and fat trees as well as all existing parallelcomputers with n interconnecting nodes consume n channels of bandwidthduring broadcasting, so the per port and bisection bandwidths do notchange substantially when broadcasting.

Massively parallel high performance computers using fat tree andcrossbar interconnect suffer from a mismatch with the softwarerequirement for non-blocking broadcast of short messages. Two of themost common network functions, Allreduce and Sync simultaneouslybroadcast one-word messages. Such broadcast uses excessive bandwidth infat-tree interconnects which results in poor system performance. Anotherfunction, termed all-to-all communications wherein each computing nodein a supercomputer frequently needs to communicate to all other nodesduring the course of a computation is an essential functional capabilityof any modern interconnect scheme. Additionally, these all-to-allmessages are typically short, being a few bytes in length. Frequentlyused algorithms requiring the all-to-all function include parallelversions of matrix transpose and inversion, Fourier transforms, andsorting. The most effective way to implement the all-to-all function isto base it on a true broadcast capability. Present systems can broadcastinformation, but only by simulating the broadcast function; thus theircapability for implementing the all-to-all function is inefficient.

A poor solution to the interconnect problem leads one directly to thegeneral assumption that the most powerful processors available should becrammed into each node to achieve good supercomputer performance, thushiding the problems inherent in the interconnect by faster processorsand higher channel bandwidth. A compromise is possible if some of theseother issues are more effectively resolved. The compromise based on amore suitable interconnect would make use of processors not quite on theleading edge of integration and performance to create a supercomputer oflower cost and power consumption with just as great, or more, overallcapability. Of course, nothing prevents one from using theultra-performance processors as nodes in the proposed systems; both costand capability would rise significantly.

Today's supercomputer architecture at most makes use of 8-waymultithreading, meaning that there is hardware support for up to 8independent program threads. Any multitasking to be found is handled bysoftware. While theoretically alleviating the communications bottle-neckproblem and helping to overcome data-dependency issues, the cure isliterally worse than the disease since the nodes now spend more timemanaging the system's tasks in software than is gained by decomposingcomplex programs into tasks in the first place. What is needed is ascalable and cost effective approach to supercomputers that range insize from a briefcase to a small office building, and in performancefrom a few teraflops to a few petaflops. (A petaflop is 1000 teraflops.)

Interconnect schemes today are invariably based on material busses andcross bars. As data rates increase and data processors become faster,electrical communication between data-processing nodes becomes morepower intensive and expensive. As the number of processing nodescommunicating within a system increases, electrical communication becomeslower due to increased distance and capacitance as well as morecumbersome due to the geometric increase in the number of wires, thevolume of the crossbar, as well as its mass and power consumption.Electrical interconnects are reaching their limit of applicability. Asspeed requirements increase to match the capacity of ever fasterprocessors for handling data, faster electrical interconnects should bebased on controlled-impedance transmission lines whose terminationsincrease power consumption. Even the use of microstrip lines is only apartial solution as, in any fully-connected system, such lines shouldcross (in different board layers). Close proximity of communicationchannels produces crosstalk, which is perceived as noise on adjacentchannels. Neither of these problems occur in a light-based interconnect.

Optical interconnects, long recognized to be the ideal solution, arestill in the experimental stage with practical optical systemsconnecting only a handful of processors. The main problem with today'soptical solutions is conceptual: they are trying to solve a morecomplicated problem than necessary. This restrictive view has itsorigins in a limited version of a task or thread: if CPU overhead isrequired to switch from a computational task to a communications taskevery time a message arrives, any conceivable computation spread acrossa multiprocessor system will soon be spending most all of its time onswitching overhead. The way around this untenable situation is to createliteral, point-to-point connections as is done for the Hypercube™ andManhattan architectures such as the Transputer™. Thus, the source anddestination of every message is determined by hard-wired connections.This idea is carried over into optical schemes where there is an emitterdedicated to every receiver and a single receiver for every emitter. Foran optical system serving hundreds of thousands of nodes, the mechanicalalignment is an insurmountable nightmare.

Over the years, a number of universities and private and governmentlaboratories have investigated free space optical interconnect (FSOI)methods for multiprocessor computing, communications switching, databasesearching, and other specific applications. The bulk of the research andimplementation of FSOI has been in finding ways to achievepoint-to-point communications with narrow beams of light from multiplearrays of emitters, typically narrow-beam lasers, and multiple arrays ofphotoreceivers. The development of vertical-cavity, surface-emittinglasers (VCSELs) and integrated arrays of VCSELs has been the mainimpetus behind research in narrow-beam FSOI area. The main problems withFSOI to overcome are alignment, where each laser must hit a specificreceiver, and mechanical robustness. U.S. Pat. No. 6,509,992specifically addresses the problem of misalignment and robustness bydisclosing a system of redundant optical paths. When misalignment isdetected by a channel-monitoring device, an alternate path is chosen.

Both unfolded configurations, where an array of emitters transmits lightacross a space to an array of receivers, and folded configurations,where the emitters and receivers lie in the same plane, have beenattempted. Most FSOI methods lack direct broadcast capability due to theone-emitter, one-receiver assumption.

Point-to-point optical communications, wherein a narrowly focused laserbeam communicates information to a single receiver, represents theextreme case of an optical fan-out of one. A variation is to split anarrowly focused laser beam using one or more beam splitters, each beamsplitting producing two beams from the original. In this way, a singlenarrow beam can be split into 2^(j) beams by j beam splitters, achievingan optical fan-out of a single narrow beam into multiple narrow, butweaker, beams. However, since the receivers are typically small devices,perhaps a tenth of a millimeter in diameter, it is difficult to achieveand maintain optical alignment of the narrow laser beam onto one or morereceivers across all but the smallest distances.

A similar method of fan-out has been achieved by use of a diffractiveelement such as a hologram that splits a single beam into a multiplicityof beams. U.S. Pat. No. 6,452,700 discloses an FSOI backplane based onholographic optical elements mounted on an expansion card. This approachalso suffers from sensitivity to alignment which is augmented bytemperature sensitivity of the hologram material that affects the sizeof the fan-out pattern. In a typical implementation of a four-node,point-to-point optical interconnect whose linear dimensions areapproximately 100 mm, the constraint on angular alignment of the narrowbeam is 1/20th of a degree. Severity of this constraint increaseslinearly with the size of the interconnect.

What is needed is a cost effectively scalable approach to opticalinterconnection that is not sensitive to alignment issues.

SUMMARY OF THE INVENTION

There is a need for the following aspects of the invention. Of course,the invention is not limited to these aspects.

According to an aspect of the invention, a process comprises operatingan optical fan-out and broadcast interconnect including: fanning-out anoptical signal from an optical signal emitter, of one of a plurality ofnodes, with a diverging element of one of a plurality of optics; andbroadcasting the optical signal to one of a plurality of receivers ofall of the plurality of nodes with a light collecting and focusingelement of all of the plurality of optics, wherein the plurality ofoptics are positioned to define an optics array, the plurality ofreceivers are positioned to define a receiver array that corresponds tothe optics array and the plurality of nodes are positioned to define anode array that substantially corresponds to the receiver array and theoptics array. According to another aspect of the invention, amanufacture comprises an optical fan-out and broadcast interconnectincluding: a plurality of nodes positioned to define a node array, eachof the plurality of nodes having an optical signal emitter and aplurality of optical signal receivers positioned to define a receiverarray that substantially corresponds to the node array; and a pluralityof optics optically coupled to the array of nodes, the plurality ofoptics positioned to define an optics array that substantiallycorresponds to the node array and the receiver array, each of theplurality of optics including a diverging element and a light collectingand focusing element, wherein an optical signal from the optical signalemitter is fanned-out by the diverging element of one of the optics andbroadcast to one of the plurality of receivers of all of the pluralityof nodes by the light collecting and focusing element of all of theplurality of optics. According to another aspect of the invention, aprocess comprises operating a lightnode including: fanning-out anoptical signal through a diverging element; broadcasting the opticalsignal through a light collecting and focusing element; and receivingthe optical signal with one of a plurality of receivers, wherein theplurality of receivers are positioned to define a receiver array.According to another aspect of the invention, a manufacture comprises alightnode including: a diverging element; a light collecting andfocusing element optically coupled to the diverging element; and areceiver array optically coupled to the light collecting and focusingelement, the receiver array having a plurality of optical signalreceivers positioned to define the receiver array. According to anotheraspect of the invention, a manufacture comprises a node array includinga plurality of nodes positioned to define the node array, each of theplurality of nodes having an optical signal emitter and a plurality ofoptical signal receivers positioned to define a receiver array thatsubstantially corresponds to the node array. According to another aspectof the invention, a manufacture comprises an optic array including aplurality of optics positioned to define the optics array, each of theplurality of optics including a diverging element and a light collectingand focusing element.

According to another aspect of the invention, an apparatus comprises acommunications network interconnect including an input layer including aplurality of input channels; a multicast channel branching fabriccoupled to the input layer; and a modular output layer coupled to themulticast channel branching fabric layer, the modular output layerincluding a plurality of individual serial data channels; and aplurality of sets of endpoints, each set of endpoints coupled to one ofthe plurality of individual serial data channels. According to anotheraspect of the invention, a method, comprises: inputting a signal into aninput layer that includes a plurality of input channels; multicastingthe signal through a multicast channel branching fabric that is coupledto the input layer; and outputting the signal through a modular outputlayer that is coupled to the multicast channel branching fabric layer,wherein outputting includes conveying the signal through a plurality ofindividual serial data channels; and sending the signal to a pluralityof sets of endpoints, each set of endpoints coupled to one of theplurality of individual serial data channels.

According to another aspect of the invention, an apparatus comprises abroadcast interconnect including: a plurality of nodes positioned todefine a node array, each of the plurality of nodes having at least oneoptical signal emitter and a plurality of optical signal receiverspositioned to define a receiver array that substantially corresponds tothe node array; and a plurality of optics optically coupled to the arrayof nodes, the plurality of optics positioned to define an optics arraythat substantially corresponds to the node array and the receiver array,each of the plurality of optics including at least one opticaldistributing element and an optical collecting element, wherein anoptical signal from the optical signal emitter is fanned-out by the atleast one optical distributing element of one of the optics andbroadcast to one of the plurality of receivers of all of the pluralityof nodes by the optical collecting element of all of the plurality ofoptics. According to another aspect of the invention, a method comprisesoperating a broadcast optical interconnect including: fanning-out anoptical signal from an optical signal emitter, of one of a plurality ofnodes, with an optical distributing element of one of a plurality ofoptics; and substantially simultaneously broadcasting the optical signalto one of a plurality of receivers of all of the plurality of nodes withan optical collecting element of all of the plurality of optics, whereinthe plurality of optics are positioned to define an optics array, theplurality of receivers are positioned to define a receiver array thatcorresponds to the optics array and the plurality of nodes arepositioned to define a node array that substantially corresponds to thereceiver array and the optics array.

These, and other, aspects of the invention will be better appreciatedand understood when considered in conjunction with the followingdescription and the accompanying drawings. It should be understood,however, that the following description, while indicating variousembodiments of the invention and numerous specific details thereof, isgiven by way of illustration and not of limitation. Many substitutions,modifications, additions and/or rearrangements may be made within thescope of the invention without departing from the spirit thereof, andthe invention includes all such substitutions, modifications, additionsand/or rearrangements.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings accompanying and forming part of this specification areincluded to depict certain aspects of the invention. A clearerconception of the invention, and of the components and operation ofsystems provided with the invention, will become more readily apparentby referring to the exemplary, and therefore nonlimiting, embodimentsillustrated in the drawings, wherein identical reference numeralsdesignate the same elements. The invention may be better understood byreference to one or more of these drawings in combination with thedescription presented herein. It should be noted that the featuresillustrated in the drawings are not necessarily drawn to scale.

FIG. 1 illustrates a schematic perspective view of a subassemblyincluding a mirror and lens array, representing an embodiment of theinvention.

FIGS. 2A and 2B illustrate schematic perspective views of light raysfrom an emitter on a wafer opposite a mirror without (FIG. 2A) and with(FIG. 2B) a diverging lens, representing an embodiment of the invention.

FIG. 3 illustrates a schematic cross sectional view of light rays froman emitter through an unfolded wafer-mirror-lens array assembly,representing an embodiment of the invention.

FIG. 4 illustrates a schematic normal view of a composite lens assemblyincluding a converging lens array and a diverging lens array,representing an embodiment of the invention.

FIG. 5 illustrates a schematic perspective view of the composite lensassembly shown in FIG. 4, representing an embodiment of the invention.

FIG. 6 illustrates a schematic normal view of an alternative compositeoptic including a converging lens and a diverging element in coaxialalignment with the converging lens, representing an embodiment of theinvention.

FIG. 7A illustrates a schematic perspective views of an enclosed opticalinterconnect assembly including a heat exchanger, a power grid, acircuit wafer, a lens array and a mirror, representing an embodiment ofthe invention.

FIGS. 7B-7C illustrate schematic side (FIG. 7B) and normal (FIG. 7C)views of the enclosed optical interconnect assembly shown in FIG. 7A,representing an embodiment of the invention.

FIG. 8 illustrate a schematic normal view of a circuit wafer including aplurality of computer nodes each of which includes four optical signalsources (emitters), representing an embodiment of the invention.

FIGS. 9A and 9B illustrate schematic normal (FIG. 9A) and side (FIG. 9B)views of an individual computer node including four optical signalsources, representing an embodiment of the invention.

FIG. 10 illustrates a schematic perspective view of a power supply busbar assembly, representing an embodiment of the invention.

FIG. 11 illustrates a schematic perspective view of two substantiallyorthogonal components of a light baffle assembly, representing anembodiment of the invention.

FIG. 12 illustrates a schematic perspective view of a light baffleassembly coupled to a plurality of individual computer nodes arranged ina wafer configuration, representing an embodiment of the invention.

FIG. 13 illustrates a schematic side view of a system including anoptical computer assembly with a partially transmissive mirror coupledto an interface array via an optical link, representing an embodiment ofthe invention.

FIG. 14 illustrates a schematic side view of an interface arraysubassembly, representing an embodiment of the invention.

FIGS. 15A-15C illustrate schematic side views of three optical computermeta-assemblies, representing embodiments of the invention.

FIG. 16 illustrates a schematic side view of a systolic optical computermeta-assembly including four optical computers, representing anembodiment of the invention.

FIG. 17 illustrates a schematic side view of fan-out (broadcast) from anoptical signal emitter via a diverging lens, representing an embodimentof the invention.

FIG. 18 illustrates a schematic side view of convergence from fan-outvia a plurality of converging lenses, representing an embodiment of theinvention.

FIG. 19 illustrates a schematic side view of convergence from amultiplicity of fan-outs via a plurality of converging lenses,representing an embodiment of the invention.

FIGS. 20A and 20B illustrate schematic normal views of single emittermodules having detector arrays configured for deployment of the modulesas part of a 5 by 5 interconnect array, representing an embodiment ofthe invention.

FIGS. 21A-21C illustrates schematic normal views of a one emitter module(FIG. 21A), a four emitter module (FIG. 21B) and an eight emitter module(FIG. 21C), representing an embodiment of the invention.

FIG. 22 illustrates a schematic side view of a single converging lens,representing an embodiment of the invention.

FIGS. 23A and 23B illustrate schematic normal (FIG. 23A) and crosssectional (FIG. 23B) views of a composite diverging-converging opticconfigured for deployment in conjunction with modules having fouremitters, representing an embodiment of the invention.

FIG. 24 illustrates a schematic perspective view of a collecting andfocusing lens optically coupled to a detector, showing a focal point anda plane defined by the detector, representing an embodiment of theinvention.

FIGS. 25A and 25B illustrate schematic bottom normal (FIG. 25A) and topnormal (FIG. 25B) views of a node including four processing nodes(modules), four emitters and 36 detectors implying deployment of thenode in a 3 by 3 node array, representing an embodiment of theinvention.

FIG. 26 illustrates a schematic normal view of a 3 by 3 module arrayshowing asymmetric alignment of the optics corresponding to the fourmodules at the upper right of the module array, representing anembodiment of the invention.

FIG. 27 illustrates a schematic perspective view of a node includingfour processing nodes (modules) each of which includes four subsections,representing an embodiment of the invention.

FIGS. 28A and 28B illustrate schematic bottom normal (FIG. 28A) and topnormal (FIG. 28B) views of a node with four processing nodes (modules),representing an embodiment of the invention.

FIG. 29 illustrates a schematic perspective view of an opticalinterconnect including a 3 by 3 node array, a 3 by 3 optic array and amirror, representing an embodiment of the invention.

FIG. 30 is a schematic view of a transmitter-to-receiver mapping for an8-way, 4-module interconnect, representing an embodiment of theinvention.

FIG. 31 is a schematic view of the conventional three layers of aninterconnect, appropriately labeled “Prior Art.”

FIG. 32 is a schematic view of a multistage fabric, appropriatelylabeled “Prior Art.”

FIG. 33 is a schematic view of an input layer showing serialization ofmessages, representing an embodiment of the invention.

FIGS. 34A-34D are schematic views of a multicast channel showing twolevels of branching and subsystems thereof, representing an embodimentof the invention.

FIGS. 35A-35C are schematic view of a switchless fabric layerillustrating channel grouping, representing an embodiment of theinvention.

FIGS. 36A-36B are schematic views of an output layer showing localgrouping of endpoints, representing an embodiment of the invention.

FIG. 37 is a face (end) view illustrating the electro-optic plane of an8-way, four module system, representing an embodiment of the invention.

FIG. 38 is an unfolded side view showing mirror and defining planes,representing an embodiment of the invention.

FIG. 39 is an illustration of a faceted lens, representing an embodimentof the invention.

FIG. 40 is a table of the symmetry properties of the broadcast lenses,representing an embodiment of the invention.

FIG. 41 is a mapping for broadcast lens 8 in FIG. 37, representing anembodiment of the invention.

FIG. 42 is a table of the symmetry properties of the 128 facets,representing an embodiment of the invention.

FIG. 43 is an illustration of the facet location parameters,representing an embodiment of the invention.

FIG. 44 is a table of Facet Parameters, representing an embodiment ofthe invention

FIG. 45 is a table of facet parameter locations, representing anembodiment of the invention

FIG. 46 is an illustration of ray geometry and system magnification,representing an embodiment of the invention

FIG. 47 is an illustration of refracted rays altering the systemmagnification, representing an embodiment of the invention

FIG. 48 is an illustration of a split lens showing offset axes of thetwo focusing surfaces (refraction of central ray ignored), representingan embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention and the various features and advantageous details thereofare explained more fully with reference to the nonlimiting embodimentsthat are illustrated in the accompanying drawings and detailed in thefollowing description. Descriptions of well known starting materials,processing techniques, components and equipment are omitted so as not tounnecessarily obscure the invention in detail. It should be understood,however, that the detailed description and the specific examples, whileindicating preferred embodiments of the invention, are given by way ofillustration only and not by way of limitation. Various substitutions,modifications, additions and/or rearrangements within the spirit and/orscope of the underlying inventive concept will become apparent to thoseskilled in the art from this disclosure.

The below-referenced U.S. patents disclose embodiments that are usefulfor the purposes for which they are intended. The entire contents ofU.S. Pat. Nos. 6,538,818; 6,509,992; 6,452,700; 6,445,326; 6,208,672;6,163,642; 6,016,211; 5,987,601; 5,965,873; 5,864,642; 5,778,015;5,703,707; 5,541,914; 5,465,379; 5,548,772; 5,546,209; 5,446,572;5,432,722; 5,420,954; 5,414,819; 5,412,506; 5,297,068; 5,228,105;5,159,473; 5,146,358; 4,953,954; 4,943,136; and 4,870,637 are all herebyexpressly incorporated by reference herein for all purposes. Thebelow-referenced U.S. patent applications disclose embodiments that areuseful for the purposes for which they are intended. The entire contentsof U.S. Ser. No. 10/175,621, filed Jun. 20, 2002 and PCT/US03/19175,filed Jun. 18, 2003 both by Brian T. Donovan & William B. Dress andentitled “Pulse Width and/or Position Modulation and/or Demodulation”are hereby expressly incorporated by reference for all purposes. Theentire contents of U.S. Ser. No. 60/290,919, filed May 14, 2001 andPCT/US02/15191, filed May 13, 2002 (published Nov. 21, 2002 as WO02/093752) all by Brian T. Donovan et al. are all hereby expresslyincorporated by reference for all purposes. The entire contents of U.S.Ser. No. 10/227,050, Aug. 23, 2002 “Dynamic Multilevel Task ManagementMethod and Apparatus” by Brian T. Donovan, Ray S. McKaig, and William B.Dress are hereby expressly incorporated by reference for all purposes.

Optical Backplane Disclosure

A massively parallel processing (MPP) system can include an array ofprocessor modules or computing nodes that are interconnected. Inpractice, each processor node is an independent die or “chip” that couldbe individually packaged and would thereby serve as a fully functionalmicroprocessor with its standard power, ground, data buses, memoryports, and so on. Much of the expense in a modern processing system liesin the packaging of an individual die and the extension supportnecessary to provide power to and communicate with each processor in thesystem. If the individual processor dies could be connected by nearestneighbor communications buses for example, and the entire array ofprocessors be retained as a single functioning module without destroyingthe wafer, it might be possible to power each processor node andcommunicate with the entire array. In this view, the wafer of processorsbecomes the computing element at a much lower cost and higher throughputthan would be incurred by separately packaging, remounting, powering,and communicating with each individual processor.

For the wafer of processors or a collection of multi-chip modules or acollection of printed-circuit board modules to be an effective andfunctional system, n integration or close geometric coupling of theindividual processor node should be implemented. Past efforts havecentered around wafer-scale bus architectures for linking all processorstogether. The disadvantages of this approach are slow communicationspeed between processors due to the long bus structures and theattendant high capacitance. Other approaches have been attempted tocommunicate between nodes using various optical methods. A recentfavorite is to have n laser emitters and n laser receivers on each nodewhere n is the number of nodes on the wafer. This point-to-pointcommunication allows each node to individually talk directly to anyother but involves a total surface area of 2n²×A, where A is the area ofan emitter or receiver, typically a region of about 100 μm on a side. Byswitching to a broadcast model where each node has a single emitter butn receivers, this overhead is cut in half. More importantly, thecommunications traffic handled by each node in the case of “fullyconnected” wafer can easily overload the computational capacity of thenode itself for both transmission and reception. In the broadcast model,where each node has but a single emitter, the transmission load isapproximately n times less while the receiving communications load canbe maximal if needed. Clearly a communications protocol should beestablished to decide whether a particular transmitted message is for aparticular node as any given emitter talks to all nodes. If the nodesare indexed or numbered for identification purposes, a map may beconstructed for each node in the array. This map specifies whichreceiver on a given node is optically linked to which particularemitter. Each receiver is then monitored by a task or a circuit runningon the node in question, said task or circuit identifying receivedmessages for the receiving node and ignoring others.

A goal of an optical backplane is to provide a parallel interconnectionstructure, connecting each node to every other node on the wafer. Oneapproach to providing such an optical interconnect is to employ an arrayof lenses and a mirror as illustrated in FIG. 1.

Referring to FIG. 1, a mirror 110 is shown on the left of the figurewith a 3×3 lens array 120 to the right of the mirror, and centered onthe mirror axis. An array of computing nodes (not shown) would lie tothe right of the lens array. The mirror 110, the array 120 and the arrayof computing nodes can all be contained within an enclosure 130,optionally under partial vacuum.

A design that optimally matches the array of nodes is to place an arrayof converging lenses where each lens has the same dimensions as theunderlying node and the array thus formed is placed directly over thearray of nodes. As shown in FIGS. 4-6, the lens array preferablyincludes both diverging elements and converging elements. The functionof the diverging elements, whether light pipes, thick optical fibers,negative conical lenses or the usual diverging (concave) sphericallenses, is to spread the light from each emitter to cover at least halfof the mirror area so that upon reflection, the emitter in questionilluminates at least the entire lens array so that every node on thewafer receives light from each emitter. This desired property isillustrated in FIGS. 2A and 2B.

Referring to FIGS. 2A-2B, a wafer 210 is depicted as the bottom diskwith an emitter 220 shown as the centered dot and a mirror 230 isrepresented by the top disk. If the emittance cone of the emitter 220 is8°, which is typical for a VCSEL laser, a set of typical rays is shownwith direct rays diverging from bottom to top and reflected raysdiverging from top to bottom. FIG. 2B is similar to FIG. 2A, butincludes a diverging lens 240 above the centered emitter 220. In FIG.2B, the entire wafer array is covered by the reflected light. Thediverging lens 220 is shown at the center of FIG. 2B as a small disk.

The invention can include inserting (including) a converging lens tocollect the reflected rays and focus the light onto the intendedreceivers. This situation is shown in FIG. 3.

Referring to FIG. 3, a cross section through the unfolded system isdepicted showing only half of the system (the light rays and lensesbelow zero are inferred by symmetry about the horizontal axis). An arrayof nodes 310 is on the left, with node centers at every 10 mm (centersare coordinates 0, 10, 20, . . . ). A mirror 320 is shown as thevertical line in the center at distance 50 from the wafer, only a singleemitter 330 at coordinate (0,0) is shown for clarity. Its accompanyingdiverging lens 340 is shown at about distance 10 from the wafer. Thelens array 350 is located at about position 90 is has its opticalcenters characterized by the spatial index reflection of the array 310on the left, the later of which is not shown in its entirety forclarity. The rays emitted from the light source at the wafer surfacediverge slightly and fill the diverging lens 340 where they spread outto cover about half the mirror 320 and then are reflected back onto thelens array 350. The diverging lens 340 further broadens the light whilethe converging lenses 355 of the lens array 350 focus the light on ornear the wafer whose reflection is shown at position 100. In FIG. 3,where the mirror is at a distance of 50 (half the wafer radius), thevariation in focal points across the wafer becomes obvious. There are atleast two ways to overcome this lack of focus across the entire wafer.The first is to place the mirror at a distance equal to or greater thanthe wafer radius, essentially flattening the surface defined by thefocal points, so the maximum deviation would be cut in half or more thanthe situation shown above. The second is to insert an array of n microlenses (not shown) just above each node, providing an additionalconvergence of the light onto the array of receivers. A microlens can beplaced just above each receiver at a distance consistent with goodfocusing of the converging beams onto the receiving photo transistors.

Referring to FIG. 4, a 3×3 array 400 of cross-shaped converging lenses410 is illustrated with a 3×3 array of smaller, square diverging lenses420 nominally residing at the lower left corner of the larger converginglenses 410. The diverging lenses 420 are represented as squares withmedian horizontal and vertical coordinate axes (defining divergingquadrants 430) drawn through their centers. The depicted array 400 couldbe optically coupled to a wafer with 9 or 3×3 nodes. For a wafer with256 or 16×16 nodes, a similar lens array could include 16×16cross-shaped lenses and 16×16 smaller, square diverging lenses fitted asshown for a total of 512 lenses. If the nodes are 10×10 mm in size, thecross-shaped converging lenses would also have outer dimensions of 10×10mm and the lens centers would be positioned precisely above the nodecenters, while the emitters are positioned at the lower-left corners ofthe nodes.

Referring to FIG. 5, a three-dimensional rendering of the array 400shown in FIG. 4 is illustrated. The smaller diverging lenses 420 areshown with contour plans in their centers. The array 400, and optionallythe array of nodes and the mirror can be contained within an enclosure510.

Referring to FIG. 6, an alternative embodiment is to center the emittersand place the (round or square) diverging element or possibly light pipeor optic fiber from the emitter passing through the precise center ofconverging lenses. The receiver map will of course be different in thiscase than in the case of corner (or edge) emitters. A planar view with acircular diverging lens is shown in FIG. 6. The converging portion issquare to just match the underlying node dimensions and an array formedfrom n of these compound lenses would sit just over the wafer aspictured in FIGS. 4 and 5.

Referring to FIG. 6, an alternative embodiment of an optic 610 includinga converging element 620 and a diverging element 630 is depicted. Inthis embodiment, the converging element 620 including a converging lensand the diverging element 630 includes a diverging lens. The diverginglens is located at the center of the converging lens and they arecoplanar.

Optical Backplane Supercomputer

The invention can include a unique, new computer architecture for theconstruction of backplane optical supercomputers composed of a multitudeof processors arranged in arrays reaching to full wafer scale sizeswhereby the individual processors are massively but inexpensivelyinterconnected and enabled to simultaneously communicate with each otherby virtue of the emission and reception of optical signals fromprocessor to processor through the use of a geometric matrix ofdivergent and convergent lenses so structured as to precisely positionthe signals and assure their proper spatial distribution through threedimensional space throughout the computer through the use of a mirroredbackplane reflective surface. With signals proceeding between thesystem's various processors at the speed of light, the invention permitsthe elimination of the wiring complexities that otherwise exist and arecompounded by the square of the number of supercomputer processor nodesas extra processor components are added in current supercomputer arraydesigns. The processors can be arrayed in planar fashion on siliconwafers or other fabrication material wafers in accordance with standardmanufacturing procedures. Each processor includes one or more gasplasma, laser, light-emitting diode (LED) or other type of lightemitting nodes together with light reception nodes. A lens matrix arraycontaining divergent and convergent lens facets for each separateprocessor is employed in planar fashion positioned at an appropriatedistance above the wafer with its array of processors. When light isemitted by any one or another of the processors, it passes through thedivergent aspect of its respective lens facet to a reflective mirrorappropriately positioned above the wafer and lens matrix. This lightthen strikes the mirror and is reflected back to and through theconvergent lens aspect of the receiving processor where it is internallyconverted to a signal for execution within that processor's processingmechanisms. The entire supercomputer system may be chilled and providedwith heat dissipation mechanisms as necessary. Software controls anddata inputs and outputs may be transmitted to and from the supercomputerby any one of a number of optical fiber mechanisms, or electrical orradio-frequency or other approaches

Wafer Scale Super Computer and Optical Switch

The invention can include the use of plasma gas discharge optical signalemitters, a fiber optical chip on wafer fiber interface and the use ofthree fibers for DWDM switch hierarchy. The invention can includecooling the wafer or other microprocessor substrate with a cooled liquidbath on the back of the wafer, preferably inverted. The invention caninclude a separable refrigerator and radiator. An operating temperatureof approximately 5° C. is easy and convenient to maintain. An operatingtemperature of approximately −50° C. is better because of lower noiseand higher speed. An operating temperature of approximately −100° C. iseven better but not all CMOS circuits work at this temperature withoutmodification. Condensation should be protected against. The wafer, lensarray, mirror and heat sink may be enclosed, optionally under vacuum; asimple glass cover bellows pressure equalized chamber is easy to use asthe enclosure and cost effective.

Powering the wafer or array of microprocessors can be done by dualconductor bus bars with a ceramic high capacity bypass capacitormaterial. These capacitive power supply strips are readily commerciallyavailable, and easy to manufacture. For instance, the amount of powercan be estimated at between 1 and 2 watts per node for 256 nodes on an 8inch wafer or 1024 nodes on a 12 inch wafer, for voltages between 1 and3 volts. With 16 power strips for 256 nodes, only 16-32 watts arecarried by any one power bus. These power buses can also act as lightbaffles and front glass/lens spacer supports. The perpendiculardirection can have just light baffle sections, which can be made ofglass or ceramic. The temperature coefficient of expansion for the powerstrips and/or baffles should be matched as well as possible to thewafers. The invention can include power busses having flexible tabs perwafer, glued or soldered to the nodes to allow for mismatched thermalexpansions.

Prototypical optics to implement the invention have been ray tracesimulated and are characterized by high efficiency in the 50-90% range.Each node can have a spreading lens or lenses over its emitter(s) andthen a focusing micro lens array over the sensor array. These lenses maybe molded glass or holographic or any other structure that provides thelight spreading and then collecting and focusing functions. Theinvention can include, a few inches above the lens array, a simple flatmirror that is located and optically coupled to the emitters, the lensesand the receivers (detectors). For a single wafer design, this simpleflat mirror can be a fully reflective front surface glass mirror.

The invention can include multiple wafers or substrates ofmicroprocessors linked by using a partially reflective mirror instead ofa fully reflective mirror and placing another wafer lens assemblyequidistant from the other side of the mirror. More wafers or substratescan be added, for example up to a total of approximately 4 with simpleoptics. In situations employing multiple wafers or substrates that aresimply linked together optically, an emission from any one processornode will be received the corresponding processor node on all of thewafers or substrates. In this case, the received power per sensorchannel is divided by the number of wafers or substrates plus opticallosses. If corresponding processor nodes send at the same time, themessage may be garbled. Therefore, embodiment of the invention that havethe potential for contention garbling, the software should be capable ofcollision handling as is done in most communications systems today.

Silicon is not a fast optical sensor material for the normal colors oflights used in optical communications. At infrared (IR) and visible redfrequencies, the light penetrates too deeply into the chips andgenerates carriers that take many 100's of nanosecond to diffuse to thesensing electrodes. An alternate way to get high speed out of silicon isto use blue or UV light. This light penetrates less then 1 um into thesensor. N carriers propagate at 200 ps/10 um, thus allowing thepossibility of very high speed sensing in standard CMOS with blue and UVlight. UV and blue LEDs are cost effective. Alternative embodiments ofthe invention can use lasers, LEDs or other emitters in CW (continuouswave) mode, and modulate them, but this is not preferred.

An alternative embodiment of the invention can use multiple emitters pernode, but with a single receiver per node. The multiple emitters can beof the same wavelength or of different wavelengths. The multipleemitters can be clustered together or spaced apart. In the case ofmultiple emitters of the same wavelength, broadcasts may require morepower and a given node may send different signals via different node atthe same time causing collisions. Although more power may be required,the light from all the emitters can be aggregated and thus much morelight can be received. Collisions can be avoided by logic processingwithin the node.

Another alternative embodiment of the invention can use multipleemitters and multiple receivers per processing node (module). This hasthe above advantage of allowing the optics to direct all of the energyfrom an emitter to a single receiver. It may be problematic to locate alarge number (e.g., 256) of emitters on each processor node.

A much less powerful alternative embodiment of the invention can usejust one emitter and one receiver per node. A simple fallbackimplementation design of this embodiment can use off-the-shelf laserchips in the red region or shorter wavelengths. Shorter wavelengths maybe desirable because red receivers are harder to make fast, whileretaining sensitivity. The invention can also include the use of one ormore frequency conversion crystal(s).

The interface to the outside world can be readily commercially availablecolor fiber optics which can be picked and placed directly onto thewafer using lower cost 850 nm lasers with one fiber per laser. In thiscase, a commercial multiplexer can be used to combine the data into asingle DWDM fiber or any other standard communications backbone. Theinvention can include the use of multiple frequency lasers. The standard850 nm recover devices can be mounted to the wafer. A cooled wafer is avery attractive option for low noise, long life and short fastinterconnect.

To provide the electro-optical interface, the invention can include theuse of embodiments disclosed in U.S. Ser. No. 10/175,621, filed Jun. 20,2002 and/or PCT/US03/19175, filed Jun. 18, 2003 for the transceiverswherever external standards do not forbid. Embodiments of the pulseposition and/or pulse width modulators and/or demodulators described inU.S. Ser. No. 10/175,621, filed Jun. 20, 2002 and PCT/US03/19175, filedJun. 18, 2003 are readily commercially available from Xyron Corporationand/or LightFleet Corporation, both of these companies having offices inVancouver, Wash., USA, and one or both of these companies are identifiedas the source of these embodiments by the trademark XADACOM™, but theinvention is not limited to pulse position and/or pulse width modulationand/or demodulation, much less these XADACOM™ embodiments.

The invention can be combined with standard fiber channels whichcurrently cost about $100-$200 per channel. For state of the art DWDM,160 channels are preferable.

The invention can include a parallel 2D interconnect wafer scale supercomputer without any inter-node free space interconnect optics, but withfiber optic interfaces. Nevertheless, preferred embodiments of theinvention include the inter-node optical interconnect, thereby allowingmassively more interconnect bandwidth. Even without the inter-node freespace optical interconnect, the invention can easily include thecapability of approximately 10 Gbaud per node throughput to nearestneighbors, for example, to four nearest edge neighbors only. Processingnodes (modules) that are not edge adjacent can send messages throughmultiple processing nodes (modules) in a sequential manner, albeit witha likely reduced throughput. With the free space optical interconnect,any node can receive from any other node without any blocking and thethroughput can be easily effected at 10 Gbaud per node.

The communication to the external fiber network, can use readilycommercially available diode lasers in chip form. VCSELS can be used forthe vertical signal source optics, and edge emitters can be used for thewafer edge optics. These edge emitters are very inexpensive at about5-10$ for each 850 nm, 3 mW output laser (1300 nm laser are about 20$,1550 nm: about 60$). The wavelength of 850 nm seems to be the mostpopular LAN choice for gigabit Ethernet and fiber channel. The readilycommercially available opto receivers at 850 nm, 1300 nm and 1500 nmwavelengths can be used in a 1-5 GHz range may be possible, but diemounted receivers may be preferable. The invention can include the useof plasma gas discharge emitters for these standard telecom wavelengths,further reducing the cost.

The context of the invention can include fiber optic multiplexingequipment connecting the wafer or supercomputer system to a network.Gigabit Ethernet and fiber channel standards are readily commerciallyavailable for the 850 nm 1300 and 1500 nm wavelengths.

The invention can include an optical computer that includes 1 wafer,several wafers, or just a few nodes cut from a wafer. Systolic arrays ofmany, and perhaps unlimited, wafers may be created with a differentrelaying lens array, that send to the next wafer, but receives from theprevious wafer. The last of the array can be looped back to the firstarray for continuous processing, optionally in a circular, torus orspherical configuration.

For a large switch application, 3 sets of external optical or electricalI/O would work well. Two of these three sets could combine 2 of theoutputs from a lower wider level of the hierarchy and 1 set would sendthe merged stream to the next higher level.

Referring to FIGS. 7A-7C, a circuit wafer 701 is coupled to a coolingstructure 705, such as a plate and/or backside bath. The circuit wafer701 includes gas plasma discharge optical signal emitters. The circuitwafer 701 is coupled to a power grid 702. The power grid can includelight baffles. The power grid 702 is coupled to a lens array 703. Thelens array is coupled to a mirror 704. The circuit waver 701, power grid702, lens array 703, mirror 704 are located within a gas tight enclosure706 that contains a suitable gas 707 such as N, H, He, etcetera. Part ofthe cooling structure 705 extends through the enclosure 706 to provide aheat sink that can be coupled to a heat exchanger (not shown in FIGS.7A-7C).

Referring to FIG. 8, a circuit wafer 801 includes a plurality ofindividual computer nodes 810. In this embodiment each of the individualcomputer nodes 810 includes four optical signal emitters 820 located atthe corners of each of the individual computer nodes 810.

Referring to FIGS. 9A and 9B, the invention can include an integratedcircuit embodied in a computer node 910, where the integrated circuitincludes one or more optical signal emitters. In this embodiment, thecomputer node 910 includes i) a wafer carrying a plurality ofmicroprocessors and ii) four optical signal emitters. The invention doesnot require the presence of the microprocessors and can include the useof any number of optical signal emitters. The optical signal emitterscan be plasma gas discharge emitters 920 or laser and/or photo diodes922. For instance, modulated VCSELs (vertical-cavity, surface-emittinglasers) can provide an alternative to the plasma gas discharge opticalsignal emitters.

Referring to the top of FIG. 9A, an adjacent computer node 923 isschematically depicted. Communication between nodes/wafers can beprovided by readily commercially available fiber-optics modules whichmay be integrated onto each node/wafer. The nodes can be spaced fromapproximately 25 um to approximately 5000 um (preferably fromapproximately 250 um to approximately 500 um) apart from one another.

Referring to FIG. 9B, a side view of the computer node 910 is depicted.The computer node can include an on chip lens array 921 (not depicted inFIG. 9A). An optical signal detector can be located beneath each of themembers of the chip lens array 921. Each of the optical signal emitterscan include an emitter lens and/or light pipe 924. The emitter lensand/or light pipes 924 of two or more emitters, together with thoseintegrated circuit emitters, can be combined to define an opticalbackplane, with or without the balance of the computer node 910components.

Referring to FIG. 10, a power supply strip 1050 includes a highdielectric insulator 1052 coupled between a first power supply conductor1051 and a second power supply conductor 1053. Although two conductorsand a single insulator are shown in FIG. 10, the strip can include 3, 4or more conductors. Both the first power supply conductor 1051 and thesecond power supply conductor 1053 include a plurality of flexible powertabs 1060 that can be electrically coupled o a wafer (nodes).

Referring to FIG. 11, a first light baffle slat 1103 includes aplurality of notches 1153 for assembling into a grid pattern. A secondlight baffle slat 1104 also includes a plurality of notches and is showninverted and perpendicular to the first slat prior to assembly. It canbe appreciated that the slats can be fabricated from power supply stripsif both exposed sides of each strip are covered (e.g., coated) with aninsulator layer.

Referring to FIG. 12, a plurality of power supply strips are shown beingassembled into a combined power supply bus and light baffle 1202 that iscoupled to a circuit wafer 1201. This combined structure, as well asindividual structures in alternative embodiments, can be connected tothe wafer directly, or to the wafer closely through tabs and/or spacers,or to the wafer in a spaced apart from relationship through leads and/orstand-offs.

Referring to FIG. 13, the context of the invention can include freespace optical coupling to other components, such as a 2D blade array1362 with edge mounted optical transceivers 1370. A computer or networkdevice 1360 includes a fan-out free spaced optical interconnectbackplane having a partially silvered mirror 1365. The device 1360 isoptically coupled to a wafer to blade array lens or lens array 1361through the partially silver mirror 1365. The wafer to blade array lensor lens array 1361 is optically coupled to the edge mounted opticaltransceivers 1370.

Referring to FIG. 14, an individual blade 1450 includes an opticaltransceiver 1463. The optical transceiver 1463 is coupled to a bladeprocessor 1464, a dynamic random access memory circuit 1465 and a harddrive 1466.

Referring to FIGS. 15A-15C, several different configurations ofcombinations having multiple fan-out free space optical interconnectbackplanes are depicted. The invention can include a two, or three,dimensional combination of multiple fan-out free space opticalinterconnect backplanes. Referring to FIG. 15A, a first optical supercomputer 1561 is coupled to a second optical supercomputer 1562 via apartially silvered mirror 1504. Referring to FIG. 15B, a first opticalsuper computer 1563 is coupled to a second optical supercomputer 1564without a mirror. Referring to FIG. 15C, four optical super computers1565, 1565, 1566, 1567, each having a partially silver mirror, arecoupled together via partially silvered distribution mirror 1544.

Referring to FIG. 16, a first optical super computer 1610 is opticallycoupled to a first alternative lens array 1682 for systolic operation.The first alternative lens array 1682 is optically coupled to a multiwafer mirror 1680. The multi wafer mirror 1680 is optically coupled to asecond alternative lens array 1683 that is coupled to a second opticalsuper computer 1612. The multi wafer mirror 1680 is also opticallycoupled to a third alternative lens array 1685 that is coupled to athird optical super computer 1614. The multi wafer mirror 1680 is alsooptically coupled to a fourth alternative lens array 1687 that iscoupled to a fourth optical super computer 1616. Thus, a systolic mirrorcan be defined as an add-drop relay mirror.

Cost Effective and Mobile Super Computing

The invention can simultaneously increase the upper limits of computingpower of the largest machines by a factor of 1000 and dramaticallyreduce the size and cost of existing supercomputing installations by anorder of magnitude. The invention is compatible with existingsupercomputer software and provides orders-of-magnitude greaterconnectivity than present-day supercomputers, obviating the need forhardware reconfigurability.

The invention can open new markets for a wide range of applications thatare now simply not possible for reasons of size, cost, or powerconsumption. Once these inventions are fully developed, it will bepossible to build a teraflop computer in the form factor of today'sdesktop computer. The world's first petaflop computer, fitting into asingle office room, could soon follow. The idea scales simply to theexaflop range allowing a truly massive, parallel machine, only dreamedabout today. Comparing these numbers to the world's currently mostpowerful computer, the NEC “Earth Simulator” at 36 teraflops (a mere0.036 petaflops), should engender an appreciation of the power of theinvention.

A further implication of these improvements in size, cost, and power, isto enable the portability of teraflop computing to on-site, mobile,airborne, or space applications where supercomputing today is simply notan option. Tremendous amounts of time and expense are consumed inremotely recording large amounts of data and transporting those data toa fixed supercomputer center where they are processed, analyzed, andacted upon. The time elapsed from collection to action is typicallymeasured in days to weeks. A portable supercomputer would allowsimultaneous data collection and analysis resulting in real-timedecisions on search vectors. This capability would greatly improve theproductivity of the equipment, compress the time to complete a giventask, and make possible the completion of tasks which today are simplynot contemplated.

The invention can allow a new generation of supercomputers to exceed, byseveral orders of magnitude, the performance-to-cost ratio of existingand planned systems. The invention can include zero-overhead taskswitching with hardware scheduling and synchronization of tasks coupledwith a high-performance data-flow architecture allows complex yetinexpensive computing nodes to be built. Optical integration of arraysof such nodes enables the possibility of a teraflop computer system in adesktop-sized package. The invention enables scaling a wafer-sizedsupercomputer to assemble components that range in capability fromteraflop to petaflop to exaflop machines.

As noted above, reliability in existing supercomputing machines becomesa major concern when there are hundreds-of-thousands to millions ofmaterial interconnections (wires, connectors, solder joints, contactbonding). If these mechanical, off-chip connections can be replaced withintegrated circuitry and light beams, both the rate of the data flowshould be greatly enhanced and the reliability of the entire systemgreatly increased.

The invention can include wafer-scale integration, a topic that has beenextensively studied for over 30 years. A wafer-scale computer system caninclude an array of processor modules or computing nodes that areinterconnected. In practice, each processor node is an independent dieor “chip” that could be individually packaged and would thereby serve asa fully functional microprocessor with its standard power, ground, databuses, memory ports and so on. Much of the expense in a modernprocessing system lies in the packaging of individual dies and thesupport necessary to provide power to and communicate with eachprocessor in the system. If the individual processor nodes could beconnected efficiently and the entire array of processors retained as asingle functioning module, it would then be possible to power eachprocessor node and to communicate with the entire array. In this model,an entire wafer becomes a computing element with a much lower cost andhigher throughput than would be achieved by separately packaging,remounting, powering, and communicating with discrete and individuallypackaged chips.

As also noted above, the problems with previous optical interconnectionschemes have been precision placement of light emitters and alignment ofthe optical elements. The solution proposed here avoids these problemsby using the inherent registration precision of wafer manufacturing,employing a broadcast model with at least a single emitter on each node,and by using an optic array for spreading a focusing light from theemitters.

Computational Hardware

The Gigaflop Node

Each individual node can include a single processor die containingmultiple processing units, communications hardware, and a localnetworking or communications bus. Specialized nodes can be devoted tomemory (RAM) supported by communication hardware and memory-controlhardware. By interspersing memory nodes and processor nodes on a waferor on alternate wafers, any desired ratio of compute-performance tomemory-capacity can be achieved.

To make efficient use of processor cycles in a single node wheremultiple clients should be serviced in a timely fashion, thezero-overhead-task switching described in U.S. Pat. No. 5,987,601 can beused in combination with a hardware-based, real-time-operating-system(RTOS) kernel. In this way, the invention can include a highlyefficient, transparent managing of hundreds of interacting tasks usingdynamic-priority scheduling. Thus, each receiver on each node could beviewed as an elementary task for that node so parallel messages over theentire node can be effectively managed. Embodiments of thezero-overhead-task switching described in U.S. Pat. No. 5,987,601 arereadily commercially available from Xyron Corporation and/or LightFleetCorporation, both of these companies having offices in Vancouver, Wash.,USA, and one or both of these companies are identified as the source ofthese embodiments by the trademark ZOTS™, but the invention is notlimited to zero-overhead task switching, much less these ZOTS™embodiments.

A computation can be broken into multiple tasks much as themultithreading processors treat programmed threads quasi-independently.Multithreading can hide some latency but requires state of the artcompiler or very clever programmers to achieve even modest performanceimprovement. The zero-overhead-task switching multitasking is a superset of the multithreading concept. It allows the latency hiding ofmultithreading, then adds dynamic priorities, and hardware semaphore forsynchronization; this is accomplished without thread-switching overhead.Zero-overhead-task switching hardware multitasking decouples the storageand switching elements of the task management, thus allowing very largenumbers of tasks, easily exceeding 256, to be stored compactly inon-chip RAM, without seriously impacting the single task clock speed andperformance. This is critical in a large, multiprocessor system wherehundreds of cycles may be required to access a remote piece of data.

The zero-overhead-tack switching processing engine makes effective useof data flow. However, in the case of the invention, data flow can be ona conceptually higher level than routing bits and microcode within acentral-processing unit (CPU). The invention can include a fullyasynchronous data-flow path connecting each of the functional modulescomprising the node. This data-flow interconnect (DFI) becomes much morepowerful and practical that the usual bus architectures in making use ofmessage packets. These packets are controlled on a local level,obviating the need for bus arbitration. The DFI bus is transparent tothe system programmer who only need worry about data destinations andnot how or when data arrives.

For a wafer including n nodes, each node can have at least one opticaltransmitter to broadcast information to the entire wafer and each nodecan have n photo-diode receivers to accept information from all nodes inthe wafer. Since each receiver has its own associated communicationsmodule that talks to the DFI bus, only packets destined for the node inquestion are placed on the node's DFI bus. The receiver's communicationmodule decodes the packet header, places the packet on the DFI bus withthe appropriate destination code, and waits for the next packet. Dataacknowledgment is routed on the DFI bus to the node's transmitterstation as required. This local processing allows asynchronouscommunication to take place without global control, greatly simplifyingthe communications protocol and speeding up data flow throughout thesystem.

For purposes of comparison with planned supercomputers, assume that thecore CPU is an 8 gigaflop (GF) equivalent Power PC™, MIPS™, or ARM™,machine that has been augmented for multitasking by with zero-overheadtask switching. As above, assume that there are multiple,special-purpose processors within each node such as the communicationsreceivers and the transmitter station that communicate with the main andauxiliary processors (FPUs, matrix processors, etc.) by accessing theDFI bus.

In summary, the main features of the node processor can be (1) thezero-overhead task switching multitasking technology allied with astate-of-the-art processor, (2) the DFI bus for intra-nodecommunications, (3) the DFI-enabled multiprocessing capability, (4) themultiple communication modules with their photo-diode receivers, and (3)the single, optical-transmitter module.

The 1000 Gigaflop Wafer

For the wafer to be an effective and functional element in a computersystem, or even a supercomputer in its own right, wafer-scaleintegration of the individual processor nodes should be achieved. Pastefforts have centered around wafer-scale bus architectures for linkingall processors together. The disadvantages of this approach are slowcommunication speed between processors due to the long bus structuresand the attendant high capacitance. Other approaches have attempted tocommunicate between nodes using various optical methods. A recentfavorite is to have n laser emitters and n laser receivers on each nodewhere n is the number of nodes on the wafer. This point-to-pointcommunication allows each node to talk individually and directly to anyother node.

By switching to a broadcast model where each node has a single emitterbut n receivers, the chip area required for communications isapproximately halved. More importantly, the communications traffichandled by each node in the case of a fully connected wafer can easilyoverload the computational capacity of the node itself for bothtransmission and reception. In the invention with the broadcast model,where each node has but a single emitter, the transmission load isapproximately n times less while the receiving communications load canbe maximal (the wafer can run with all nodes transmittingsimultaneously).

In addition to the optical-based broadcast mode of communications, eachnode on the wafer communicates with its nearest neighbors in the usualfashion. That is, each node has four data buses (north, south, east, andwest) so that the entire wafer is connected in a Manhattan grid. This“grid bus” not only provides an alternative path for messages but may beused for diagnostics as well as systolic-array applications.

Clearly, a communications protocol should be established to decidewhether a particular transmitted message is for a particular node sinceany given emitter talks to all nodes. If the nodes are indexed ornumbered for identification purposes, a map may be constructed for eachnode in the array. This map specifies which receiver on a given node isoptically linked to which particular emitter. Each receiver is thenmonitored by a circuit or task running on the node in question, thistask identifying messages for receiving node and ignoring all others.

Messages across the wafer are delayed only due to the finite speed oflight and the length of the modulation sequences. Present-day machinesrequires message passing or a means of relaying from node to node formessages to across an array of processors.

The wafer broadcast model also makes use of the data-flow model in thatthe material DFI bus is now replaced with light. Data is accepted by areceiver on a target node if that data packet is addressed to that node.This allows controlled point-to-point communications to be achievedwithin the broadcast model as well as broadcasting system-wideinformation from a single transmitter. Hierarchical control of aninter-wafer communications is then a matter of software rather thanspecialized hardware.

More than 256 dies of dimension 10 by 10 mm can fit on a 200 mm diameterwafer and over 600 such dies can fit on a 300 mm wafer (the area of the300 mm wafer is 2.25 times larger than a 200 mm wafer). Larger dies meanfewer nodes, of course, but more area for additional processors andsupport circuitry per node. This trade-off between the number and sizeof the nodes is a key variable in the design equation for tailoringsupercomputer installations for specific uses.

In summary, the features of the wafer module can be (1) its full,optical, global interconnect based on a designed optical interconnect;(2) local interconnect on an x-y (Manhattan) grid; and (3) one or moremodulated light emitters on each node.

The Teraflop Briefcase

A single 300 mm (12 inch) wafer with optics can fit into a space of 12inch by 12 inch by 4 inch plus room for access hardware (wires,connectors, etc.), housing and mechanical support, and auxiliaryhardware. With 2 to 8 GF nodes, the performance figure would be between1 and 4 teraflops (one teraflop is one thousand gigaflops) and dependson the silicon technology use. Such a package would fit nicely inside abriefcase and consume a few kilowatts of power, making a fully portabledevice (battery powered with a heavy-duty auxiliary battery pack).

Two wafers facing each other through a half-silvered mirror comprise afully connected system of 1024 processors. The nodes on wafer A can talkto each other by reflection from the mirror or talk to wafer B bytransmission through the half-silvered mirror; a similar situationobtains for wafer B with respect to wafer A. At 8 GF per node, theperformance figure for this configuration is approximately 8 teraflops.Power consumption would be between 1 and 100 KW depending on designparticulars (choice of silicon technology and clock speed). For thelow-power version, the cooling fluid could be a gas such as helium oreven air. In the high-power configuration, the can be bonded to aforce-cooled heat-sink, for instance a copper plate. The size of thepackage would be about that of a thick briefcase—about 12 inches by 15inches by about 8 inches thick. At a kilowatt, battery operation wouldrequire an auxiliary package; the faster versions (up to 8 teraflopswith present-day technology) would not support portable operation, butrequire external power and additional cooling in the form of a highheat-capacity fluid and a heat-exchange system.

A similar system based on multi-chip modules (MCMs) or printed-circuitboards (PCBs) having 10 optical communications nodes arranged as a 2 by5 array of optical communication nodes, with each communication nodesupporting four processing nodes (modules) each, and each processingnode (module) having quad 8 GF processors can be built today. Such adevice would also fit into a standard briefcase and consume about 1kilowatt of power and have a peak performance of over 1 teraflop.

In summary, a briefcase version of a teraflop supercomputer is not onlyconceivable but achievable with today's component technology. Trueportability depends on battery and cooling technologies and desiredauxiliaries such as storage, input, and output devices.

The 200 Teraflop File Cabinet

A convenient cabinet containing 300 mm wafers, optics, and cooling canbe about 0.5 m on a side by 1 m in length. Spaced at 20 cm apart, therecan be 50 such wafers in a cabinet, giving a total of approximately25,600 processor nodes in a cabinet. This is about twice the number ofprocessors in the AP 100-TF machine, yet, due to theoptical-interconnect feature, the invention can take up far less spaceand power. Wafer-to-wafer communication can also be by wire connectionsor SONET-like optical interconnects for those wafers not facing eachother.

Wafers, interconnects between wafers, cooling plates, and mountinghardware all contribute to the weight of the teraflop cabinet. Theestimated total weight is about 150 kg for a fully functional cabinet,excluding power supply and cooling.

In summary, the main features of the cabinet system can be its (1)mounting and cooling systems, (2) on- and off-cabinet fiber-opticcommunications, and (3) modularity of function and design.

The Petaflop Room

A small room containing 5 to a few dozen of the cabinets will provide acomputing power in the petaflop (PF) range. (A petaflop is one thousandteraflops or one million gigaflops.) Five cabinets, taking up a fewsquare meters of floor space, yield a 1 PF computer while two dozen suchcabinets in a single layer would require about 120 sq. ft. of floorspace, 5 megawatts of power, and result in a performance figure of about5 petaflops. In contrast, previously planned versions of a petaflopmachine are considerably larger and more power-hungry than the machineenvisioned here.

Interconnection between the cabinets can be by standard fiber-opticcommunications technology with transmitters and receivers integrated onthe wafers themselves. Multiple fibers between cabinets, with severalfibers between each wafer, can fully connect one stack of wafers toanother using the same zero-overhead-task switching and DFI technologiesas described above.

The Exaflop Suite

One quarter of a million wafers, 512 nodes per wafer, 8 GF per nodegives a 1 exaflop (EF) total performance figure. (An exaflop is onethousand petaflops, or one million teraflops, or one billion gigaflops.)A convenient cabinet, as discussed above, contains 50 wafers, meaningapproximately 5000 such cabinets in all, for a total volume of 1250 m³.Stacked three layers high to form 1.5 m high units, the floor spacecovered by these 5000 cabinets will be approximately 833 m² (excludingaccess corridors), or about the floor space of an office suite (lessthan 9000 sq. ft.). The interconnections can be optical (light beams)and contained in the spaces between the wafers along with the powergrids and cooling fluid as described above. Although such a machineoccupies an area equal to the ASCI Purple, it weighs 3 to 4 times more.However, the specific area and weight (per teraflop) is several thousandtimes less than ASCI Purple in area and several hundred times less inweight. This extreme contrast underscores that this new family ofsupercomputers can easily span the range from the portable to themassive using the same modular technology and zero-overhead-taskswitching based DFI interconnect.

The specific power consumption is about 30 kW/TF for AP and is about 2kW/TF for the invention, depending on the processor used. This isapproximately 15 times lower than AP and still considerably better thanBGL. However, the specific power density (watts per cubic meter perteraflop) of the invention is even more favorable, being less than onehundredth of that of the AP. The processing density of the invention,primarily due to the wafer-scale integration, is between 2 and 3 ordersof magnitude higher than AP. The total cost is expected to be about thesame to 10 times more for a full scale embodiment of the invention thanfor the AP, while the specific cost (in dollars per teraflop orprice-to-performance) is two to three orders of magnitude more favorablefor the invention than for the AP. This extreme contrast in specificpower and price performance underscores the essential affordability ofthe invention.

In summary, the main points of the inventive family of supercomputersare (1) wide scalability as evinced by the specific size, cost,capability, and power consumption, (2) modular construction; (3)inherently low cost, and (4) high reliability of opticalinterconnections.

Auxiliary Hardware

Optical Interconnect

A significant feature of the wafer-scale interconnect system is a lensarray that both spreads the light from each individual emitter andcollects this spread light, reflected from a plane mirror back onto thewafer, focusing light beams onto each of the individual photo-diodereceivers. The emitters themselves should be modulated light sources inthe form of gas plasma discharge devices, light-emitting diodes (LEDs)or solid-state lasers.

In the invention, light from each emitter illuminates the entire waferafter reflection from a mirror held parallel to the water surface. Acompound-lens array focuses this light on to each node. Since theemitters are varying distances from a given target node, the focalpoints at the target node are at different locations, effectivelyimaging the array of nodes onto each node in the array. An additionalmicrolens array can be placed just above each node so that the focusedlight from the main lens array is further concentrated on the individualreceiver photo-diodes distributed across each node.

Mass Storage & RAM

In addition to local memory at each node, each wafer may be serviced bya conventional RAID array or blade computer including a single CPU(perhaps the same processor as used on the wafer), mass storage andrandom-access memory as needed. Some configurations may require a singleRAID array or blade computer per cabinet, while others may need one ormore servers per wafer. A supercomputer used primarily as a video orimage server might require more mass storage than one configuredprimarily as a weather simulator, for example.

This marriage of the blade computer or RAID array with the wafer levelfree space fan out optical backplane interconnect concept dramaticallyincreases the flexibility of configuring a supercomputer out of standardcomponents yet tailored to specific applications. Interconnectionoptions could be built in to the modules, allowing a given installationto easily reconfigure its hardware to solve a wider range of problems asthe need arose. This is a variation on the scalability issue where onedesign tends to fit a very wide range of needs.

Communications

Connections to the outside world (console devices, other computers, thehigh-speed internet) can be by standard, off-the-shelf fiber opticsmodules and components. Indeed, each wafer or certain designated waferscan have integrally mounted optical modulators and demodulators for suchfiber communications.

Power Considerations

For the briefcase model, there will be 256 nodes per wafer running about5 Watts per node. Thus, a wafer will dissipate about 1.25 kW of power.Increasing this to 512 nodes per wafer and a power density approachingthat of the Power PC or Pentium™, (upwards of 100 W per node) means awafer will dissipate about 50 kW per wafer. With 50 wafers to a cabinet,65 kW should be removed for the low-end system and over 2.5 MW from thehigh-end system on a per-cabinet basis. Therefore, the space required bythe cooling system may be roughly the same as required by thewafer-containing cabinets.

This heat is distributed across each wafer and should be removed in sucha fashion as to keep the entire wafer at a uniform and reasonably lowtemperature. Two different approaches are suggested: (1) circulate acooling fluid throughout each cabinet such that each wafer is uniformlycooled and (2) mount each wafer or pair of wafers on a copper-alloycooling plate, each plate having a cooling fluid circulated to, throughand away from it. The cooling-plate solution has an additional advantageof forming a superstructure for precise mounting of the opticalcomponents.

Software

Operating System Software

This primary operating system for the invention can be Linux, configuredto handle multiple modes as ccNUMA capable processors executing a singleoperating-system image. A single Linux 2.6 image can be run on eachwafer, allowing 65,000 to 130,000 tasks under a single Linux image to bemanaged across a wafer. Optional operating system software supported caninclude packages capable of creating Beowulf clusters, a proventechnology for building supercomputers from clusters of Linuxworkstations.

Communications Software

Low overhead communication between nodes can be implemented using theemitter-receiver optical technology outlined previously. This technologycan underlie the ccNuma implementation, and may be exposed for use byprogramming libraries (e.g., MPI), or for direct usage by bespokeapplications.

Compilers

The inventive system can provide standard compilers for languages suchas C, C++, Java, etc. For scientific computing, languages like HPF,Fortran90, and Fortran77 can be supported, as can extended versions of Cand C++. The invention can include compilers that can generate code tothe particular strengths of the inventive architecture, includingoptimization to map intermediate representations of dataflow to the finegrained zero-overhead-task switching multitasking.

Programming Libraries

Various portable supercomputing libraries, such as OpenMP, MPI, and PVM,can provide portable programming APIs for supercomputer applications.

System Management

When very large machines are built, supercomputers or otherwise, thereis a requirement for system management packages. For the invention,there can be packages for system backup, system volume management,hardware fault detection and isolation, resource allocation, and systempartitioning.

Multitasking and Hypertasking

The invention can include zero-overhead task switching (e.g., ZOTS™) andthe hardware methods for managing a multitasking system based ondynamically changing task priorities and round-robin schedulingdisclosed in U.S. Ser. No. 10/227,050, filed Aug. 23, 2002. Embodimentsof hardware methods for managing a multitasking system based ondynamically changing task priorities and round-robin schedulingdescribed in U.S. Ser. No. 10/175,621, filed Jun. 20, 2002 are readilycommercially available from Xyron Corporation and/or LightFleetCorporation, both of these companies having offices in Vancouver, Wash.,USA, and one or both of these companies are identified as the source ofthese embodiments by the trademark hwRTOS™, but the invention is notlimited to a hardware method for managing a multitasking system based ondynamically changing task priorities and round-robin scheduling, muchless these hwRTOS™ embodiments. A hardware, real-time operating systemmay be thought of as an essential kernel of a real-time operating system(RTOS) embodied in hardware. The combination of zero-overhead-taskswitching and hardware methods for managing a multitasking system basedon dynamically changing task priorities and round-robin scheduling,enables on-chip multitasking to be performed with optimal efficiencysuch that all CPU cycles are applied to the computational task and nonewasted on management overhead functions. Potential costs of someembodiments of the invention are latencies associated with prioritymanagement and silicon area required for the circuitry. The former istypically a few gate delays while the latter scales as n in n tasks.These costs remain negligible for up to 512 tasks per node, meaning thatthe benefits of fine-grained multitasking are achievable for a widerange of applications for very little cost.

The same multitasking idea manages communications and messages betweennodes on a wafer and between wafers. At the wafer scale, hardwaremethods for managing a multitasking system based on dynamically changingtask priorities and round-robin scheduling, residing on each node meanshundreds of thousands of individual tasks across the system areavailable for fine-grained decomposition of difficult problems; the term“hypertasking” distinguishes this pan-wafer task management andswitching from on-chip multitasking. In a supercomputer configuration,many of these tasks, to be sure, will be dedicated to handling themyriad messages that must crisscross the wafer, but a substantialportion will be available to the programmer, allowing greatercomputational efficiency than presently achievable. For example, certainsupervisory nodes on each wafer will be responsible for multitaskdecomposition of code fragments. These supervisors then distribute themultiple tasks across the wafer or the entire system as necessary.Interplay between various nodes concerning issues of priority,scheduling, and task completion communicated by the optical backplane tosupervisory nodes form the logical basis behind hypertasking, which maybe thought of as distributed but inter-coordinated multitasking.

Hypertasking allows the effective degree of parallelism to besignificantly higher than previous computational models once theinterplay between software and the hardware-enabled multitasking areunderstood and used to advantage.

Data Flow Interface

The data flow interface (DFI) architecture allows multiple processors,some of which can be small and dedicated, to reside on a single nodewhile retaining effective and efficient data pathways between thefunctional parts. Imagine an asynchronous, high-speed bus connecting theCPU, multiple FPUs, math coprocessors such as multiply and accumulatesor MACs, communications-stack processors, and other functional units.Enough local intelligence resides in the DFI to achieve dynamic routingof data packets, allowing control messages and data to directly reachdestinations without traveling over circuitous paths. This flow ismanaged locally within the DFI, freeing the CPU for more useful work.Local control means that specialized hardware modules typically used forDMA and bus control, so essential in conventional architectures, are notrequired in DFI-based zero-overhead-task switching machines.

It is envisioned that each photodiode receiver station will reside onsuch a data path and be managed by a local task or stack processor.Since the communications system operates in broadcast mode, mostmessages received at a given station will probably be meant for anothernode. Local processing of data packets ensures that messages will notcollide nor delay one another even though all nodes may besimultaneously broadcasting information. Messages not meant for thereceiving node are simply ignored; as such they do not contribute to DFItraffic within that node.

Optical Backplane

What is not often realized, is that the synchronization and coordinationbetween the set of receivers and set of emitters is also a verydifficult problem when fine-grained multitasking should be avoided. Itis important to appreciate that the two problems of point-to-pointconnectivity and message synchronization are solved by a broadcast modelcoupled with the zero-overhead-task switching and DFI techniques.

A fully connected wafer of processors has never been attempted. Such atask involves a nightmare topology of interconnect busses andbus-arbitration devices. Any implementation would involve multiple metallayers and require enough wafer area as to lower the processor density.The only practical approach to full and direct interconnect is optical.The invention can include a broadcast model where each node has oneemitter that is optically connected to all other nodes on the wafer. Alenslet placed above each emitter forms a shaped light beam before thebeam reaches the diverging element residing in the main compound-lensarray. As explained above (Optical Interconnect), a compound lens arrayis placed between the wafer and a mirror. This array both spreads thelight from each emitter so that it illuminates the entire wafer uponreflection and focuses light onto each node's receiver array. Anadditional n×n lenslet array can sit atop each node to adjust the focusof the main, compound-lens array onto each of the photodiode n²receivers on each node. These several lens arrays may be opticalholograms, cast optical elements, or assembled from individual lenses.

The zero-overhead-task switching approach addresses the problem ofmessage synchronization by replacing issues of strict communicationcoherency with fine-grained tasks that allow asynchronous messaged toflow from node to node. The broadcast concept allows messages to crossan entire wafer in a single step whereas the point-to-point opticalinterconnect requires nearly twice as much hardware to accomplish thesame result and introduces message delays due to the relaying process.

Parallelism Issues

A good way to finesse Amdahl's law has not yet been found. Since theserial portion of a calculation dominates the time to perform thecalculation as the number of processors increase (Amdahl's law), oneshould redefine the serial portion so that it may be more effectivelyexecuted. While respecting the serial nature of a given problem, it ispossible, in many cases, to speed up any sequence of serial steps bymeans of multithreading. The zero-overhead-task switching architecturewith its priority-based task scheduling forms the basis for afine-grained superset of multithreading, yielding a substantial speedimprovement over simple, high-level multithreading. The result is aneffective way to circumvent Amdahl's law since an erstwhile serialportion of code, if written at a sufficiently abstract level (removedfrom hardware), can be decomposed into a large number of small tasksthat have little or no dependencies. The result is an apparentparallelism of a serial section of code in that the processor executingthis code runs at greatly enhanced efficiency due to removal of memoryand data-access latencies achieved by hardware-controlled inter-taskreshuffling.

In carrying this latter idea across processing nodes (modules), it iseasy to see that the zero-overhead-task switching concept enablesparallel algorithms to perform at their optimum. First, decomposing agiven problem into a set of parallel and serial portions allows eachportion to be efficiently mapped onto a set of fine-grained tasks whichare then managed and coordinated by the hardware task manager across aset of nodes and executed with little to no overhead by thezero-overhead-task switching mechanism. Second, hardware multitaskingavoids latency associated with message passing and communicationsbetween parallel tasks. This, in turn, alleviates the problem associatedwith inter-node data dependencies in the same fashion as above.

The zero-overhead-task switching and hardware methods for managing amultitasking system based on dynamically changing task priorities andround-robin scheduling, mechanisms allow efficient and effective use ofmultitasking within nodes and hypertasking across a network of nodes.The result is lower latency, a method of handling data dependencies, andmore effective use of all processors in the system. Additionally,auxiliary hardware found in conventional supercomputers fordirect-memory access, bus hardware and controllers, cross-bar mechanismsand controllers, system broadcast modules, and the like are simply notneeded since the functions performed by the specialized hardware listedabove are effectively performed as software tasks in a priority-managedsystem based on zero-overhead-task switching and hardware methods formanaging a multitasking system based on dynamically changing taskpriorities and round-robin scheduling. The absence of the suite ofcommunications hardware greatly reduces the need for complicatedcommunications software.

The broadcast model coupled with the compound lens array means highertolerance to mechanical misalignment, eliminates the need of strictcoordination between messages, and achieves faster communications atlower power and cost. Material busses and cross bars are eliminatedmeaning that less hardware and power dissipation are required; theresult is lower overall system cost.

The combination of these technologies, innovations and off-the-shelfcomponents results in a scalable, modular supercomputer system thattakes advantages of economies of scale and allows dynamicreconfigurability far beyond that of present and planned machines.

Thermal Considerations

Commercial off-the-shelf MMC (metal matrix ceramic) such as copper withpitch based graphite can be matched to the coefficient of thermalexpansion of silicon and conduct heat away from the circuits and towarda heat sink. The invention can also utilize a gold eutectic bonded tothe circuits or wafer. In addition, the wafer can be thinned ifnecessary. The invention could include the use of a wafer made from puresilicon-28 isotope which has a 60% improved thermal conductivity.Preferred embodiments of the invention can operation at temperatures offrom −50 to 25 C, held to within 1 degree. Based on a calculated thermaldifferential for a 200 um thick silicon wafer at 5 kW dissipation and 1degree C. estimates a cost of approximately $1000 per 5 kW wafer for achiller.

A more complicated version of the invention can include a clear coolingbath placed on the front side of the wafer as well. In that case, if gasplasma discharge devices were used as the signal emitters the gasdischarge cells could include roughly 2 mm diameter microspheres filledwith an appropriate gas at the appropriate pressure.

Power Supply

The need for 5 KW at 1.5V and 4000 A is non-trivial. Preferredembodiments of the invention can include a full 3-phase solution at 400VAC in a standard “Y” configuration. Unisolated direct PWM buckconverter to 1.5V. Multiple stages may be used if necessary, but themain point for cost is to avoid the use of active transistors or diodesat the 1.5 voltage level. The final filtering can be done with smallpassive inductors and capacitors (using a 1 MHz switching frequency).Isolation is desirable, albeit at added cost and weight, and should bedone in the first stage, by converting the 400 VAC to 48-120 VDC.Calculations indicate that the power supplies can be about the size ofthe PC power supply for each wafer. Of course, the invention can useconventional off the shelf power supplies.

To minimize writing losses at the low voltages, the power suppliesshould be mounted within a foot or so of the wafer. A 1 cm (0000′ gauge)copier wire can go from the power supply to the copper graphite MMCwafer TCE matched xy power grid. To provide a large amount of bypasscapacitance, barium titanate dielectric or other high capacitancematerial can be integrated into the power plates. Dead and shorted nodescan be removed via laser. Wafers with too many bad nodes, can be cut upand used as standard IC's.

Mechanical

Matching thermal coefficients of expansion is important to reliableoperations. Pitch derived graphite in a copper or Al matrix, can bematched to any thermal coefficients of expansion from the base metalcoefficients to −0.002 ppm/K.

Optical alignment requirements are in the 0.3 mrad or about 100 micronsvertical edge to edge for a 12 inch wafer. In view of the fact that theinvention can include cooling and controlling the temperature of theentire assembly, there will be no trouble achieving the opticalalignment needed. For instance, the invention can be embodied in an 8inch high by 13 inch square processing box, with a half inch IDinsulated cold liquid input and an uninsulated half inch ID output tubegoing to a chiller.

Mounting of conventional off the shelf laser die and IR receivers can beimplemented using standard pick and place systems. The invention caninclude the use of standard IC process wire bonding pads to easealignment requirements. For example, silver filled epoxy has enoughflexibility to accommodate the TCE differences inherent in theseconnections.

Testing

The high speed integrated optical receivers can be testing using a smallsolid state laser attached to a testing head that uses the broadcastmode to illuminate all 512 photodiodes at once while probing the waferto insure that all receivers work. Many companies including Agilent makeoptical testing heads, so they are readily commercially available.

Pick-and-Place of Optoelectronic Die on Wafer

The invention can including pick and place of a chip onto a 12 inchwafer with 30 micron xy accuracy and the inclusion of a precision dropof conductive silver adhesive. Equipment that can place within +5microns is readily commercially available.

Optical Interconnect Layer

As previously discussed, it has long been recognized that electricalinterconnect methods are approaching their limit in spite of advances inphoto-lithography and the miniaturization of high-speed electrical delaylines. Another way of viewing the situation is that electricalinterconnects are reaching a limit whereas free-space opticalinterconnects continue to scale according to an optical Moore's Lawdependent on the information capacity of modulated light and theachievable density of photoreceivers. The inherent advantages of opticsrests on the non-interference of light in free space. While fiber opticsretains some of the disadvantages of electrical delay lines, namely thephysical space occupied by the fibers or electrical wiring, free-spaceoptical communication has no such disadvantage.

The invention overcomes most all of the problems and difficulties ofpresent approaches to FSOI by making simultaneous use of two keyconcepts, that of optical fan-out and broadcast. Both of these conceptshave been widely recognized as enabling ideas for FSOI, however theyhave yet to be combined into a unified approach. The novel lensstructure disclosed here allows both fan-out and broadcast to becombined in a simple and inexpensive yet powerful FSOI.

The invention provides a way of fully interconnecting a plurality ofassociated circuit modules lying in a plane or other geometricconfiguration. Conceptually and functionally, the circuit modules aregrouped into heterogeneous functional sets, which may be termed a nodeor processing node or processing module, whether or not the set performscomputations in the sense of a computer. A multiprocessing system caninclude a number of processing nodes linked by either electrical oroptical connections, or a combination of the two. The invention can bebased on a free-space optical interconnect (FSOI) between multiplenodes. Associated with each node are one or more emitters (transmitters)and one or more detectors (receivers). If there are n communicatingnodes in a system, there can be n emitters and n(n−1) receivers, or n(n)receivers if desired. Each emitter broadcasts information via opticalfan-out to all other n−1 nodes in the system. Each node also has areceiver for each of the other n−1 nodes in the system (or for n nodesby allowing each node to communicate with itself, in which case theinformation is broadcast to all n nodes in the system). The mapping ofthe entire set of n emitters to the receivers within a single node isone-to-one so that the simple presence of a message at a receiverautomatically identifies the emitter or source of the message. However,since each emitter is broadcasting to all of its receivers when sendinga message, the desired destination of a message may be ambiguous. Thatis, a given message might be meant for all nodes in the system, aparticular subgroup of nodes, or a single particular node. Thisambiguity can be resolved by supplying each message with a short headerthat identifies the intended recipient. This message header may bedecoded by circuitry located at the receiver site. A message for aparticular receiver will then be passed on to a subsequent stage ofprocessing. Any message not intended for a particular receiving node issimply ignored. Message contention or collision is not an issue in theinterconnect described herein.

Optionally, there can be one or more modules associated with each node.If there are two or more modules associated with a node and two or moreemitters associated with that node, then each of those emitters can beassociated with one, or two (or more) of those modules. (If there isonly one emitter associated with a node, it can be associated with allthe modules associated with that node.) For instance, if there are fourlaser diode emitters associated with a node and four computationalprocessing modules associated with that node, then each of thecomputational modules may have a one-to-one association with one of thediode emitters. Further, each of the optical signal detectors associatedwith that (multi-module associated) node then needs to query not merelywhether an incoming received data signal is addressed to that node, butwhether and to which of the four associated modules that incoming datasignal is addressed.

This new broadcast capability should lead to substantial performancegains as a percentage of peak performance. The broadcast method derivedfrom the invention is a simultaneous non-blocking broadcast capabilityfor short messages. While the 8-byte bandwidth provided by the inventionis already over 100 times higher than in competing systems, the peakbroadcast bandwidth is a multiple, by the number of communication nodes,beyond. For a 64-communications-node system, this translates into a peakbroadcast bandwidth of over 7 gigabytes per second per communicationsand a peak bisection broadcast bandwidth of 448 gigabytes per second,all based on commercial Sonet OC48 electro-optical components operatingat 2.5 gigabits per second. This unexpectedly advantageous result is dueto the ability of all 64 laser transmitters to optically broadcast toall receiving nodes where each individual receiver or pixel(s) has anassociated short-message buffer.

Optical Fan-Out & Broadcast

The invention has been reduced to practice and demonstratesinterconnecting large numbers of processing elements within a smallvolume. The invention makes use of optical fan-out wherein a singlelight emitter can broadcast its signal to multiple receivers. Although agiven emitter can broadcast to multiple receivers efficiently andeffectively, a single receiver should not receive information from morethan a single emitter, otherwise message contention as well as confusionof origin can arise. Electrically, this fan-out function would beachieved by an electrical fan-out or multiplexing circuit, oftenreferred to as an electrical cross bar, along with buffer amplifiers foreach pathway from a given emitting node. Optically, a simple way toaccomplish fan-out is by spreading the output of an emitter with anoptical element and then refocusing portions of the fanned-out beam withmultiple collecting lenses. Since a broadcast message reaches allreceiving nodes in the system nearly simultaneously, a destination codeis required to identify the desired recipient or recipients of thetransmitted message; such a code is necessary for broadcasting messagesboth electrically and optically.

FIG. 17 illustrates the concept of optical fan-out. The broadcastapproach disclosed herein is both simultaneous (to all nodes in thesystem at the same time) and non-blocking (multiple nodes maysimultaneously broadcast information). In this document, “broadcast”will be taken to mean “simultaneous, non-blocking broadcast” unlessstated otherwise.

Referring to FIG. 17, fan-out (divergence) from a light source isdepicted. The light source 1710 is represented by the circle at the leftof the figure. The shaded triangle with apex at the light sourcerepresents the inherent spread or divergence of the light beam from thelight source. The light source (emitter) can be one, or more than one,optical signal emitter(s). The optical signal emitter can be gas plasmadischarge optical signal emitter, a light emitting diode and/or a laserdiode or any other signal emitting capable light source. In the case ofmore than one emitter, the plurality of emitters can define a cluster ofoptical signal emitters. The cluster can include emitters that operateon different frequencies to enable frequency (wavelength or color)multiplexing and/or emitters that operate on substantially the samefrequency to enable parallel output power aggregation. (Similarly, thelight receiver (detector), described elsewhere in more detail, candefine a cluster of receivers, of the same or different types.)Throughout this document, when the terms emitter or receiver (or theirequivalents) are recited, the corresponding clusters that can be definedare deemed to also be described.

Still referring to FIG. 17, a spreading element 1720 can increase thefan-out of the original light beam to cover an entire set of collectionand focusing optics that are described elsewhere and shown in otherfigures. The spreading element 1720 can be one, or more than one, lensor any other light diverging capable optical spreading structure. Thespreading element 1720 can include a concave lens, a concave-concavelens and/or a convex-concave lens. The spreading element can include aFresnel lens. The spreading element can include a holographic element.

Light from each emitter in the interconnect can undergo an initialoptical fan-out by integral optics that are coupled to the emitter(s),such as a spreading and shaping lens commonly packaged with one or moregas plasma discharge emitters, lasers or light-emitting diodes (LEDs).Further, the integrated optic and emitter can be integral with thecircuit(s) that provide the signal and/or the power to the emitter(s).In the invention, fan-out can be increased as needed through the use ofone or more optic(s) placed in line with the emitter and preferablylying substantially in the plane of the light-collecting optics. (Theselight-collecting optical elements will be described in more detail in asubsequent section.)

Once the light from an emitter is sufficiently spread out so as to coveror illuminate an entire set of receiving elements, or at least a subsetof the receiving elements, the light should then be sufficientlyconcentrated so that individual receiving elements (e.g.,photoreceivers) will have sufficient intensity to allow detection of thesignal being broadcast. If the originating light beam is sufficientlypowerful, then no additional concentrating element is required. Such anarrangement is practical only for broadcast to a set of receivers lyingwithin a small area. The larger this receiving region, the more powerfulthe light source should be to supply sufficient power to each detector(e.g., photoreceiver).

The invention overcomes the problems of inadequate light intensity atthe receivers as well as the problem of maintaining precise alignment ofthe emitter beam with the receiver position by a novel configuration ofdiverging and converging optics. In contrast to the usual approach tothe FSOI problem, maintaining a precise direction of the emitter beam isno longer a critical parameter. In the invention, a critical parameterbecomes the position of the emitter with respect to the set ofreceivers; something that is relatively easy to achieve inprinted-circuit boards (PCBs) and multi-chip modules (MCMs). Thelithographic processes presently used in fabrication of siliconmicro-electronics are at least an order of magnitude more precise thanneeded to achieve the accuracy that is required for the invention. Thus,the constraint on beam direction in point-to-point systems is replacedby the easier-to-achieve positional constraint provided by theinvention.

Registration of the image of the array of emitters with each receiverarray depends on the placement and design of a lens structure above eachreceiver array. The constraint on the placement of this structure isprimarily lateral in nature and should be met to within a fraction ofthe receiver spacing, something that is again relatively easy to achieveusing mounting posts or stand-offs precisely located on the PCB or MCM.All location and angle tolerances in the system disclosed herein areroughly multiplied by the optical power of the lens structure. Forexample, if an array of emitters of linear dimension d is focused ontoan array of receivers of linear dimension r by the system optics, alinear tolerance of t mm becomes t d/r mm, where d/r is typicallypreferably approximately 10 or greater. Thus, if the constraint is tomaintain beam focus on a receiver to within 50 microns, the placement ofthe lenses or mounting posts or other elements should collectivelycontribute no more than 0.5 mm to the misalignment. This is a tolerancethat is quite easy to achieve.

Referring to FIG. 18, a form of optical multiplexing is enabled withoutthe need for multiple amplifiers or buffers as in the case of anelectrical multiplexer or fiber-optic star multiplexer. FIG. 18illustrates how information from a single emitter can be broadcast tomultiple receivers using a set of light-collecting and focusing (e.g.,converging) elements.

FIG. 18 illustrates optical broadcast from a single emitter located atthe apex of the cone of light on the left of the figure, representing anembodiment of the invention. The light from this single emitter has beenfanned-out by appropriate optics not shown in this figure (e.g., adiverging concave-concave Fresnel lens). An array of light-collectingand focusing optics 1810 is represented by the column of ovals shown onthe right side of the figure. Each element 1820 of the light-collectingand focusing optics 1810 can be one, or more than one, lens or any otherlight converging and focusing capable optical spreading structure. Thelight-collecting and focusing elements 1820 can include a convex lens, aconcave-convex lens and/or a convex-convex lens. The light-collectingand focusing elements 1820 can include a Fresnel lens.

Fanned-out light incident on each collecting optic can be focused onto aphotoreceiver located at the apex 1830 of the light cones to the rightof the optic array. Thus, light from a single emitter is made availableto multiple receivers through the use of fan-out with the result thatinformation contained in the light is broadcast to all receivers thatlie at an appropriate focal point of the collecting optics. It can beappreciated that the receivers can be located in a coplanar arrangement.Any particular receiver can ignore a message by examining a code (e.g.,header in a broadcast packet) designed to specify message destination,and determining that the message is ear-marked for another node. Thecombination of the fan-out and multiplexing nature of the exemplary lensstructure disclosed in this document comprises a particular approach ofachieving a fully interconnected, broadcast, optical-interconnect systemand the invention is of course not limited to the described examples.

Optical Interconnect

The invention significantly avoids joining and splitting problemsassociated with confined light beams as in light pipes or fiber optics.Moreover, the invention significantly avoids the more severe problemsassociated with electrical interconnects and point-to-point FSOImethods.

Referring to FIG. 19, a set of three emitters A, B, C are located on theleft side and a set of receivers are located on the right side of theillustration. FIG. 19 illustrates the concept of broadcasting opticalinformation from a plurality of emitters to a plurality of receivers.All three of the fanned-out signals from emitters A, B, C are collectedand focused by the set of light collecting and focusing optics 1910. Itis important to appreciate that FIG. 19 represents an “unfolded”configuration wherein the emitters and receivers lie in differentplanes. It is possible, and it is a preferred embodiment of theinvention, to employ a folded configuration wherein a mirror is placedsubstantially parallel to a plane containing both the emitters and thereceivers. FIG. 19 can adequately represent a folded configuration bysimply imaging the mirror to lie precisely halfway between the emitterplane on the left and the receiver plane on the right, with itsreflective side towards the emitter-receiver array. In thisinterpretation of the graphic, the illustration has been unfolded, notthe device itself and the receiver array on the right is the mirrorimage of the actual receivers which lie in the plane of emitters on theleft. Please note that the sequence of A, B, C on the left from top tobottom is reversed to c, b, a on the right from top to bottom,consistent with a (reversed) mirror image. Where convenient, an unfoldedgraphic will be used to illustrate both folded and unfoldedconfigurations of the optical interconnect.

Referring to FIG. 19, fan-out from multiple sources falling on the sameset of collecting and focusing optics 1910 is depicted. This opticalmultiplexing establishes an optical fabric that connects n sources ton×m receivers in broadcast mode, where there are m receiver arrays inthe system (n need not equal m). Each emitter is labeled by anupper-case letter (A, B, C) on the left. Each of the set of receiverarrays 1940 on the right (7 are depicted in FIG. 19) receives light fromeach of the three emitters. The individual receivers are labeled bylower-case letters (c, b, a). Since light from mutually incoherentsources does not interfere at an optical element and light fromdifferent sources does not interfere in free space, light reaching aparticular receiver, say any of the a receivers, originates only at asingle emitter (A in this case).

The mirror element (not shown in FIG. 19) need not be a specularlyreflecting device such as a first-surface, metalized glass substrate. Itis possible to replace the mirror with a diffuse reflector as found in amovie or projector screen. In this screen implementation, the light fromthe emitters is not spread out, but kept in narrowly focused beams. Thearray of beams then impacts the screen in a precise grid of points. Eachbeam then undergoes a diffuse reflection from the screen and illuminatesthe entire array of collecting lenses. More light is lost in thisapproach than in a specular reflection from a metalized mirror, so theemitters should be correspondingly brighter. Alignment is more difficultin this case as each emitted beam should be directed precisely onto alocation on the screen to within an accuracy that is approximately halfthe size of the active portion of a receiver (usually a few hundredmicrons or smaller) multiplied by the optical power as explained above.The angular constraint on the parallelism of the plane of the screenwith the plane of the receivers remains as before, but the overalleffect of an optical broadcast interconnect is achievable.

The arrangement of emitters, receivers, lenses, and mirror or screenform the optical backplane or fabric that interconnects each processornode optically to every other processor node in the computing cluster.The fundamental concepts that allow this interconnect method to functioneffectively and efficiently are the aforementioned optical fan-out andoptical broadcast. This document discloses several methods to achieveeffective optical coupling between emitter and receiver stations.

The Preferred Lens Structure

A goal of the invention is to provide a method of optically imaging anarray of emitters onto multiple arrays of receivers. Each receiver arrayshould lie in the image plane of an optic that views the entire emitterarray. A single node or group of nodes or circuit modules communicatingwith a receiver array lying in the focal plane of a single collectinglens, including the receiver array, the collecting lens and any requiredoptics for spreading the output from one or more emitters can be termeda lightnode. The lens structure associated with a lightnode both spreadsout the light from the emitter so as to illuminate the entire array ofnodes and images light from all emitters in the system onto theparticular receiver array of that lightnode.

Typically, a node has one emitter for each processor node (module),although this is not a required constraint as processing nodes (modules)can have more than one light emitter each, or may well share lightemitters by temporal multiplexing. The receiver array belonging to alightnode may belong to a single processing node (module) or be sharedamong a group of processing nodes (modules) that may be associated withthe particular lightnode.

In one embodiment of the invention, each node has an associated emitterand an associated receiver array. Any of a variety of configurations arepossible under the constraint that each receiver array is configured asan image of the entire array of emitters. Two possible emitter andreceiver configurations are shown in FIGS. 20A and 20B.

Referring to FIGS. 20A and 20B, two of many possible configurations forthe front surface of a node having but a single emitter are depicted.The single emitter is shown as the open circle and the receivers as thearray of black dots centered in the larger square, which represents theboundary of the face of the node. The corresponding lens structure (notshown) lies above the plane of the page.

In both FIGS. 20A and 20B, the receiver array is centered in the nodeface. FIG. 20A shows the node's emitter 2010 above and to the left ofthe receiver array 2000. Here, the lower-right receiver 2015 in the nodereceives light from that node's emitter. In the node face layer depictedin FIG. 20B, the emitter 2020 is placed in the center of the receiverarray 2030. The image formed by the node's lens structure maps its ownemitter's light back onto the emitter 2020, however this causes noproblems since this particular light path is not focused by thecollecting optic that lies directly above the emitter, but spread twiceby the diverging optic. This action also occurs in FIG. 20A, but thecentral ray from the emitter 2010 to the mirror and back through thecenter of the collecting optic, which is centered above the receiverarray, actually reaches the receiver 2015 on the lower right.

Although a node can contain any number of emitters and processing nodes(modules), practical considerations usually limit this number to 1 or 4or 8. The larger the number, the more processing nodes (modules) arerequired to receive information from each receiver in a node. At somepoint, the electrical fan-out circuitry connecting multiple circuitmodules to a single receiver becomes unwieldy. Several configurationsare illustrated in FIGS. 21A-21C

Referring to FIGS. 21A-21C, three preferred embodiments of node facesare depicted. The large, open circles represent emitters and the arraysdots represent the receiver arrays. The embodiment depicted in FIG. 21Ahas an emitter multiplicity of 1, and shows a single emitter 2110 andits associated receiver array 2120. It can be appreciated from the 5×5configuration of the members of the receiver array 2120 that this nodeis configured for deployment as part of an array of 25 nodes. If theemitter 2110 is shared by more than one module, than each of thereceivers in the receiver array 2120 will need to determine if anincoming signal is for any of the more than one modules. The embodimentdepicted in FIG. 21B has an emitter multiplicity of 4 and is a morepreferred embodiment of a node configuration. Four emitters 2131, 2132,2133, 2134 are located outboard the corners of the receiver array 2140.It can be appreciated from the 6×6 configuration of the members of thereceiver array 2140 that this node is configured for deployment as partof an array of 9 nodes. If each of the four emitters 2131, 2132, 2133,2134 is associated with one of four modules, than each of the receiversin the receiver array 2140 will need to determine if an incoming signalis for any of the four modules. The embodiment depicted in FIG. 21C, hasan emitter multiplicity 8. The eight emitters 2150 are located in aspaced apart relationship around the perimeter of the receiver array2160. It can be appreciated from the configuration of the members of thereceiver array 2160 that this node is configured for deployment as partof an array of 4 nodes. If each of the eight emitters 2150 is associatedwith one of eight modules, than each of the receivers in the receiverarray 2160 will need to determine if an incoming signal is for any ofthe eight modules. Each of these three arrangements may be repeated inan array of nodes where the spacing of emitters in such an array hasregular and uniform spacing so that the image of the emitters is aregular array of focal points that is set to match any of the receiverarrays in the system.

In a more preferred embodiment of the invention, each node has amultiplicity of 4 meaning that there are 4 emitters associated with eachnode. These emitters can be spaced as shown FIG. 21B. The spacing shownallows a square array, for example, of nodes to be assembled where thespacing between emitters is the same across the array in both verticaland horizontal directions. The face of the nodes can be square, thisbeing a most convenient form, but the invention is not limited to squareface nodes.

The advantages of a multiplicity-4 array of nodes over an array having asingle emitter per node is that there is 4 times the light intensity perunit area for a given sized array and 75% fewer receivers in the entiresystem. The overall system size depends, among other factors, on thephysical dimensions of the receivers. Thus, a multiplicity-4 array ofnodes can occupy roughly 75% less area than a multiplicity-1 array.Although there are also 75% fewer lens structures, these structures(optics) are typically larger since the each now contains 4 fan-outelements. On the other hand, keeping the mirror close to thereceiver-emitter plane so as to limit the physical dimensions of theinterconnect then requires lens elements with larger numericalapertures.

An important element of the optical interconnect can be a lens structurethat effects simultaneously the fan-out of individual emitters toachieve broadcast of messages and the spatial de-multiplexing ofintermingled messages carried in the various light beams onto thevarious receiver arrays as illustrated in FIG. 19. Since light from theplane of emitters is focused on the plane of receivers, which lies asclose to the emitter plane (or, equivalently, the folding mirror liesclose to the plane containing both emitters and receivers), the optimallens design for imaging the emitters onto a receiver array should bedesigned with finite conjugate focal lengths as illustrated in FIG. 22.

Referring to FIG. 22, conjugate focal lengths defined by the convergingelement of an optic are depicted. In a typical lens, the focal length,f₁ is at infinity (for a parallel beam of light), while f₂ is 50 mm in atypical camera. For an exemplary converging element 2210 for use in anoptic of a lightnode, f₁ is the distance from the emitter 2220 to thelens and f₂ is the distance from the lens to the receiver 2230. Thesedistances may be quite different depending on the inherent spread in theemitter 2220 and the optic required to adjust this spread.

Each lightnode can have an associated focusing lens as illustrated inFIG. 22. Light from all emitters in the array of nodes falls on thelens, which is idealized as the shaded region to the left in FIG. 22.The function of the lens is to focus all incident light onto a receiver2230 in the face of the node; this is represented as the shaded regionto the right of FIG. 22, where the receiver 2230 in question lies at theapex of the shaded region on the far right. In a preferred embodiment,this collecting and focusing optic can be an aspheric, Fresnel lens withconjugate focal lengths that match the dimensions chosen for the opticalinterconnect system.

Since the set of emitters on the face of a node should illuminate theentire node array and the collecting and focusing lens should be asefficient as possible so as to reduce the requirement for optical powerof each emitter in the system, the diverging light from the emitters andthe converging light to the receivers should pass through the sameoptical system. This presents an inconsistency since any convergingelement will focus light incident from either side of that element. Thesolution to this dilemma is to place a “spreading aperture” in theconverging lens to allow light from an emitter to pass through theregion of the converging lens without being focused. If the inherentdivergence of an emitter allows light to reach the entire array of nodesand is not so great as to demand a large aperture through the collectingoptic, a simple hole in the collecting optic will suffice. It is usuallythe case, however, that the light emitted from the devices mostconvenient for the implementation of the invention emerges within afairly narrow cone of a few degrees, and with an oval cross section.Compensating optics can be placed at the emitter and produce a circularspreading beam of a few degrees. When this beam reaches the position ofthe lens structure, it may be a few mm in diameter. Allowing it tospread to cover the entire array of nodes usually requires a distancemany times larger than practical. In this case, the spreading aperturecan contain a small diverging lens that may also correct for anelliptically shaped beam should that be necessary. A multiplicity-4,Fresnel lens structure is illustrated in FIGS. 23A-23B.

Referring to FIGS. 23A-23B, a compound lens structure 2300 for a singlelightnode (module) servicing four processing nodes (modules) isdepicted. FIG. 23A is a top view of a Fresnel lens structure designed tospread out four emitter beams using four Fresnel lenses 2311, 2312,2313, 2314 which are depicted as the four smaller sets of concentriccircles. The light-collection portion 2320 of a lens structure caninclude a square section of a large-diameter compound aspheric Fresnellens or a smaller-diameter Fresnel lens lying within a square. Thedimensions of the square match those of the surface of the node face foroptimum light-gathering efficiency. FIG. 23B shows a cross section ofthe compound Fresnel lens structure 2300. A multiplicity-1 lensstructure to match the structure depicted in FIG. 20A would have thethree small Fresnel lenses depicted in FIG. 23A (upper left 2311, lowerright 2313, and lower left 2314) removed with the grooves of the largelens continuing into those regions.

The light-collection part of a lightnode's lens structure is generallyany structure capable of gathering and focusing light such as sphericallenses, aspheric lenses, diffractive elements (binary optics andholograms), light funnels, and so on. A particular embodiment is can bean aspheric, compound Fresnel lens specifically designed with twodifferent conjugate focal lengths as shown in FIGS. 23A-23B. The overalldesign constraints are to minimize the volume occupied by the light(determined by the area of the lens structure and the sum of itsconjugate focal lengths) while allowing an optimal size for the array ofreceiver elements (receivers should be placed far enough apart tominimize or reduce cross talk between focal points and should be placedclose enough to ensure that the array fits within the desired area onthe face of a node).

Aspheric Lens Design

The design equation for an aspheric lens surface is given by

$\begin{matrix}{z = {\frac{{\kappa\rho}^{2}}{\sqrt{1 - {\left( {k + 1} \right)\kappa^{2}\rho^{2}}} + 1} + {\sum\limits_{j = 1}^{m}\;{\alpha_{j}\rho^{j}}}}} & (1)\end{matrix}$where z is the height of the lens surface above the x-y plane and hasdimensions of length. κ is the curvature and has dimensions of inverselength and ρ is the axial distance from the lens axis measured in thex-y plane and also has dimensions of length. The expansion coefficientsα_(j) have dimensions of inverse length to the power j−1. The parameterk is dimensionless and lies between −1 and +1. For k<0, the lens has ahigh aspect ratio (k=−1 produces a parabolic surface). A spherical lensresults for k=0, and a low-aspect ratio lens with steep edges for k>0.

The parameters κ, k, and the coefficients α are selected by aminimization or evolutionary programming process to minimize the focalregion of the lens at the desired distance. Referring to FIG. 22, thefirst step is to consider the focal point at f₁ and the lens surface onthe right with parallel rays incident from the right. The designequation is used to concentrate the parallel bundle of rays tracedthroughout the right lens surface using Snell's law of refraction. Asfew expansion coefficients as are required to accomplish this task arechosen. Once a lens surface that correctly focuses the left-travelingparallel rays has been found, a left lens surface is then placed asshown in the figure and a new bundle of rays is traced from the focalpoint on the left, through the first lens surface (left surface) intothe material of refractive index n and thence through the second lenssurface (right surface). For this step, a new set of surface parametersfor the left surface are chosen. The parameters of the right surface arethen varied. This process is repeated until the bundle of raysoriginating on the left of the figure at focal length f₁ are properlyfocused at conjugate focal length f₂ on the right of the figure. In thecase of a Fresnel lens, the surface height z is stepped as shown in FIG.23B before rays are traced through the system. This process generallyconverges fairly quickly to a satisfactory set of parameters that thencan be used in the manufacturing process.

Asymmetric, Aspheric Lens Design

The above design process produces an axially symmetric lens that isoptimized for both light source and focal point situated on the axis ofthe lens. In the optical interconnect disclosed here, most light sourcesare far from the lens axis. This is especially true for large systemswith many emitters and receiver arrays. To accommodate off-axis sources,a given lens can be made slightly asymmetric so that it is biasedtowards focusing light whose source is a point lying away from the lensaxis. Equation 1 expands the lens surface in a simple polynomial in ρ.Replacing the sum over powers of ρ with a sum spherical harmonics allowsa general representation of a surface that is not necessarily axiallysymmetric. Such a surface will have lumps or bulges to correct foroff-axis light sources.

The design process to asymmetrize a lens is to first design an axiallysymmetric lens as in the previous section. To this approximate lenssurface add a spherical harmonic of the formα₂(A²−ρ²)×ρ⁻¹ or α₂(A²−ρ²)(x²−y²)ρ⁻²  (2)where α₂ has units of inverse length, A is the aperture radius,ρ=(x²+y²)^(−1/2), and x and y are Cartesian coordinates in the planewith z the axis of the lens. The coefficient α₂ is adjusted as describedabove to place the lens focus of an off-axis source at the desiredposition and minimize the focal region, which will now exhibit coma andspherical aberration. This process may be repeated with the nextspherical harmonics of the next higher order until the desiredtolerances on the focal position and size of the focal region areachieved. Any reference on orthogonal expansions, such as OrthogonalFunctions by G. Sansone, Dover Publications, New York will provide thenecessary functional forms for use in this procedure.

Light Budget for a Square Array of Nodes

The light from each emitter should be spread so that every receiver isilluminated. In practical terms, this implies that the lens above eachreceiver array should be sufficiently illuminated by each emitter in thesystem. Unless optics, such as prisms and optical wedges, are used, thelight from any emitter should effectively span the largest dimensionacross the array of nodes. If the array is square or rectangular inshape, this dimension is the diagonal. If the array is circular, thisdimension is the diameter of the circle. This maximum dimension of theplanar array is reduced slightly by the twice distance of an outsideemitter to the edge of the array. Thus, if the emitters are as shown inFIGS. 20A-20B or FIGS. 21A-21C, and the node face is a 50×50 mm square,the reduction is approximately 25(2)^(−1/2) mm. If there are 25 suchnodes arranged in a square, the radius of the light cone, when reflectedto fall back onto the array of lens structures, is (2)^(−1/2)(5×50−25)mm or approximately 320 mm. Without optics to fold back light that wouldotherwise fall outside the node array upon reflection or miss the mirrorentirely, the light will be uniformly spread over an area of about320,000 mm², assuming a uniform illumination within the emitter beam.Since the maximum area of the collecting lens, in this example, is 50×50mm² with a 10 to 20% reduction for the area required by the divergingoptics, the fraction of light falling on any lens structure and hencefocused onto any receiver is the ratio of these two areas, or about0.8%. This is further reduced by reflective losses and irregularities inthe various optics.

In a square array with the light-collecting per node area proportionalto the dimensions of the face of the node, the fraction of lightcollected is given by

$\begin{matrix}{\frac{2}{\left( {{2n} - 1} \right)^{2}\pi}ɛ} & (3)\end{matrix}$where n² is now the number of nodes in the array and ∈ is the efficiencyof the optics and accounts for reflective losses, loss in area due tothe diverging optics (the small lens inserts shown in FIGS. 23A-23B),and any empirical imperfections in the optics. Typically, ∈ is about 0.4for the multiplicity-4 structure (see FIG. 21B) and 0.3 for amultiplicity-1 lens (see FIG. 21A).

The typical, commercially available photoreceiver has a sensitivity ofabout −21 dBm (about 8 μW of optical power). The active region is in theneighborhood of 0.2 mm on a side for an area of 0.04 mm². Ideal opticswould focus the image of each emitter precisely onto a spot of 0.2 mm indiameter centered on the photoreceiver. If the spacing betweenphotoreceivers is a small fraction larger than their width, any smallimperfections in focus or alignment, or any mechanical vibration, wouldcause unwanted cross-talk between receivers. From a mechanical alignmentand robustness perspective, it is a good idea to place thephotoreceivers as far apart as possible within the constraints imposedby the physical size of the node face. Robustness against misalignmentand mechanical instabilities is then achieved by focusing the light inan area centered on each receiver. Of course, an additional micro lensmay be placed just above each receiver to concentrate the spread-outbeam onto the receiver.

Suppose the configuration constraint is to choose anemitter-to-corner-receiver distance to be the same as thereceiver-to-receiver distance, then a node such as depicted in FIG. 21B(i.e., four emitters or a multiplicity of k=4), would have a spacing ofs/2(2n+1) between receivers where s is the dimension of the side of thenode face. This is shown in the node depicted in FIG. 21B with n=6. Theoptimum diameter of the focused spot is now s/2(2n+1) instead of themore restrictive 0.2 mm. The ratio of the areas of the optimum-diameterspot to the ideal spot is the excess power factor needed to adjust theemitter powers so the receivers have adequate power with thismechanically optimum receiver spacing. For small arrays, the spot sizecalculated by this method is usually larger than the 1 mm or so that issufficient to satisfy all but extreme cases of misalignment orvibration. For larger arrays, this spacing can be in the few hundredmicron range, indicating that custom-designed and fabricated receiverarrays are required.

Mechanical Stability & Focal Spot

If the collecting and focusing optic is placed at the optimal positionwith respect to the receiver array, each emitter image formed by theoptic will lie in precise registration with the corresponding activearea of each receiver. Since the receivers are typically a few tens ofmicrons in diameter, and a larger area implies a slower response, theoptimum focus position is also the most unstable to lens imperfections,mechanical misalignments, and mechanical vibrations. Such imperfectionswill lead to momentary loss of communications while misalignment tomechanical shock may lead to permanent loss of communications. By movingthe collecting and focusing optic closer the receiver array, the focalpoint on the node face becomes a focal region surrounding the receiver'sactive area. The optimal diameter of this focal region is the spacingbetween receiver centers. Of course, the light intensity at a receiveris lower within the focal region than at a focal point with the smallerdiameter of the receiver's active area. To compensate for this loss ofintensity at the receivers, more powerful emitters can be used.

The distance from the node face layer to the plane of the lens structurecan be adjusted to establish the proper focal region. The configurationof regions is shown in FIG. 24.

Referring to FIG. 24, the concept of under focus is depicted. Thecollecting and focusing optic 2410 is represented by the large oval onthe left. The dot on the far right is located at the focal point of theoptic 2420. The cone of light 2430 is represented by the triangularshaded area and the receiver in the plane of the node face 2440 by thesmall white oval. The dotted oval surrounding the receiver lies in theplane of the node face and shows the extent of the focal regionassociated with the each receiver 2450.

By choosing a lenslet array to include converging lenslets (positivefocal length), the array of lens structures can be placed closer to thenode face. On the other hand, an array of diverging lenses (negativefocal length) allows the array of lens structures to be placed fartherfrom the node face. Such fine-tuning might arise when the divergence ofthe emitters needs to be matched to a certain sized diverging optic inthe lens structure.

Electro-Optical Layer

To achieve an efficient coupling of n nodes, each emitting and receivingmodulated light in a broadcast mode, where each node can receive opticalsignals from every other node simultaneously, an optical system isrequired. First, the optics should sufficiently spread out light fromeach emitter so that each receiver is illuminated. Second, this mixtureof light from all emitters that falls onto each receiving node should bespatially de-multiplexed into separate beams so that each node receivesa distance light beam from each emitting node. This can be accomplishedby the optical interconnect layer disclosed herein.

The next stage in establishing an interconnection of an array ofprocessing modes should consider the conversion of electrical signals tobe sent from processing elements to optical signals for transmissionwithin the device. This stage also needs to consider the reception ofoptical signals by a suitable optical structure, and a conversion of theoptical signals back to electrical signals for use by the processingelements.

The receivers and emitters, along with associated drivers and amplifierscomprise the electro-optic portion of the node. These parts can bemounted on a printed-circuit board (PCB) or a multi-chip module (MCM)substrate; this submodule can be termed the electro-optic (EO) layer.The context of the free-space, optical fan-out broadcast interconnectdisclosed herein can include an electro-optical interconnect thatperforms an electrical-to-optical (EO) conversion as well as anoptical-to-electrical (OE) conversion. The optical interconnect is thestructure that interfaces the EO portion to the OE portion so that theresulting system has the desired property of establishing fast andefficient communication channels between processing nodes (modules). AnEO layer including emitters, receivers, and associated electronics isdepicted in FIGS. 25A-25B.

Referring to FIGS. 25A-25B, a node face 2550 is depicted in FIG. 25B andthe node back 2500 is depicted in FIG. 25A. The node face 2550 isdepicted without the lens structure, which would be mounted onstand-offs above the face 2550 shown in FIG. 25B. These illustrationsshow a conceptual rendition of an MCM node with the EO layer in FIG. 25Band the processor nodes 2510 (modules) in FIG. 25A. The shaded squaresin FIG. 25B represent the circuitry necessary for transductingelectrical signals for conversion to and from light signals. Thiscircuitry can include serdes (serializer-deserializer) elements 2560.Other modules 2570 contain the necessary transimpedance amplifiers,decoding circuitry, and any required local storage. The four opencircles represent the four emitters, one serving each processor node.The black dots represent the photo-receivers, one for each emitter inthe system. A fully functional interconnect for a multiprocessing systemwill also include logic and local memory for routing and temporarystorage of messages.

Simple and Compound Lightnodes

Typically, a lightnode has one emitter for each processor node, althoughthis is not a required constraint as processing nodes (modules) may wellshare light emitters by temporal multiplexing. A lightnode also containsan array of receivers that belong to a single processing node (module)or are shared among a group of processing nodes (modules) associatedwith the particular lightnode. If the emitters and receivers lie in thesame plane, the emitted light passes through the array of lensstructures before it reaches the mirror which folds the light back ontothe collecting optics.

As previously noted, a preferred embodiment of a node in the inventionincludes four emitters. In this case, a receiver array services fourprocessing nodes (modules) by local (within the node) electrical fan-outfrom each receiver to all four processing nodes (modules) and electricalfan-in to each receiver from all processing nodes (modules). Local logicwithin this electrical multiplexing of signals from receivers toprocessing nodes (modules) controls the multiplexing switches byallowing information destined for a particular node to reach that node.

As also previously noted, advantages of an interconnect constructed frommultiplicity-four nodes (four emitters to one node) include a factor of4 less receiver arrays and associated circuitry within the system, 4times the light intensity at any given receiver for an emitter of agiven power, and four times fewer nodes and associated lens structures.Other advantages include a larger node face with more space for thereceivers. This also implies that the daughter cards for the processingelectronics (discussed in the section on processing nodes) can belarger. Disadvantages are that the lenses are larger implying that thenumerical apertures of the individual collecting lenses should be largerfor a given mirror distance.

Each lightnode should contain local multiplexing circuitry in additionto the header-decoding circuitry. The lens structures are more complexin containing four diverging elements instead of one. By increasing thenumber of processing nodes (modules) per lightnode beyond 4, theelectrical multiplexing issues become more severe and the wire lengthsbecome longer. At some point, diminishing returns of advantages overdisadvantages will arise. Certain configurations of processing nodes(modules) are better met with multiplicity 4 or multiplicity 8lightnodes in spite of the rising disadvantages.

Emitters

Emitters may be lasers, groups of lasers of different wavelengths,light-emitting diodes, plasma light sources, or any other structure thatis capable of supplying modulated light, whether visible, infrared, orultraviolet. Each emitter or light source within a compound emitter(cluster or group) requires driving (modulating) circuitry to modulatethe device itself or an external structure capable of modulating lightemitted by the device.

Receivers

Receivers may be photodiodes of suitable sensitivity. A receiver may besensitized to a particular wavelength by design as in U.S. Pat. No.5,965,873 by Simpson et al. or by a wavelength filter placed over thereceiver either separately from or integral with a light-collectingmicrolens. Receivers based on photomultipliers and photo-sensitivechannel plates are also possible approaches to light detection for theinvention.

Receiver Array

The electronics (transimpedance amplifiers, limiting amplifiers, anddeserializers) associated with a lightnode's receiver array may beintegrally contained with the receivers or separately bonded to acircuit board containing the receivers and emitters. An integratedreceiver array or a discrete array of receivers may be covered by amicrolens array to gather more of the incoming light onto each receiverelement.

Methods of Light Modulation and Demodulation

U.S. Ser. No. 60/290,919, filed May 14, 2001 and PCT/US02/15191, filedMay 13, 2002 (published Nov. 21, 2002 as WO 02/093752) all by Brian T.Donovan et al. all disclose generating electrical pulses of widthsprecisely controlled to sub-cycle precision. Donovan et al, U.S. Pat.No. 6,445,326 discloses approaches to providing sub-cycle precision inmeasuring pulse widths. Dress and Donovan, U.S. Ser. No. 10/175,621,filed Jun. 20, 2002 and PCT/US03/19175, filed Jun. 18, 2003 bothentitled “Pulse Width and/or Position Modulation and/or Demodulation”disclose modulating and demodulating electrical or optical pulses withsub-cycle precision. By applying aspects of these modulation anddemodulation technologies directly to the laser driver for modulationand at the receiver array for demodulation, it is possible to achieve aspectral efficiency significantly greater than 1. Thus, the bandwidth ofthe optical interconnect disclosed herein can be increased by 4 or 8 ormore times over that of simple pulse-amplitude modulation of light aspresently practiced. The choice of which modulation and demodulationtechniques to utilize in an embodiment can be made based on achievinghigher data rate and achieving higher noise immunity.

The laser drivers may be directly modulated or modulating signals may beapplied to acousto-optical devices positioned after the light source,whether lasers, light-emitting diode, plasma, or other such source oflight. Pulse-width demodulating circuitry may be integrated with thereceiver array, allowing an inexpensive and compact receiver arraycomplete with electronics to be achieved.

Additional light modulation may achieved by using modulatedradio-frequency signals to drive an acousto-optic element as in U.S.Pat. No. 5,146,358 by William M. Books. Such modulation and attendantdemodulation can achieve higher signal-to-noise ratios and increasedsensitivity over the simple modulation and demodulation discussed above.

Lens Placement

Since light impinges as different angles depending on the source andlocation of the lightnode within the lightcube, lens structures allcentered over their receiver arrays will image the array of emitters atdifferent locations with respect to the center of the node face.However, ease of manufacturability suggests that a single design for thenode face be replicated and identical parts be used to construct theinterconnect system. There are several ways to overcome the problemimposed by the manufacturability constraint being inconsistent with thefact that different lightnodes receive light at different angles. Sincethe effect of different reception angles appears as an opticaldistortion of the image plane that contains multiple images of the arrayof emitters, an optical correction is possible by replacing the planarmirror with a spherical mirror centered over the center of the array ofnodes. The method preferred in the present embodiment, however, is toposition each image of the array of emitters so that the image is inperfect registration with the receiver array and each receiver array iscentered in the face of its node for ease of manufacturability. Thisrequires a translation of the collection optic of the lightnode's lensstructure in a direction towards the center of the array of nodes and atan amount proportional to the distance of a given lightnode's receiverarray from the center of the EO array. An example of this translation isillustrated by FIG. 26 and can be term asymmetric optic alignment.

Referring to FIG. 26, the placement of lens structures for a 3×3 nodearray is depicted. The lens structure belonging to the center lightnodeis placed precisely at the center of the receiver array as shown by thebold, circled cross 2610 in the center of the FIG. 26 since the lensstructure is illuminated symmetrically from all directions in that thereis an equal amount of light coming from the left of the vertical dottedline and impinging on the center lens structure as there is light comingfrom the right. Two of the other three axes of symmetry are also shownas dotted lines through the center of the figure. The position of thelens structure in the upper-right corner is shown by the bold, circledcross 2620. Note that this center is no longer at the center of thereceiver array 2625, represented by the array of 36 small circles in theupper-right lightnode square. Two other lens-structure centers areshown, one to the right of the center and the other above the center.The marked positions 2630, 2640 are closer to their respective receiverarrays than the center in the upper right, but are still biased towardsthe center of the figure. This asymmetric optic alignment when appliedto all of the non-central optics results in the image of the array ofemitters being in substantially perfect registration with all of thereceiver arrays. In an alternative embodiment of the invention, one ormore of the receivers can be spatially biased (asymmetricallypositioned) with regard to the node array and/or the optics array toimprove registration of optical signals with the plurality of receiversthat define the receiver array.

Processing Layer

The optical interconnect or backplane or fabric disclosed hereinprovides a simple and effective solution to fully interconnecting largenumbers of intercommunicating functional elements or circuit modules.The set of elements can be homogeneous or heterogeneous in theiroperation on the received messages or data. Examples of homogeneousprocessing elements would be a supercomputer including a large number ofidentical computing nodes or a communications switch likewise includinga large number of identical identification, correction, and routingnodes. A heterogeneous system might have a mixture of general-purposecomputing nodes, as well as specific purpose nodes for carrying out suchfunctions as encryption and decryption, message-traffic analysis, imageprocessing, mathematical functions such a matrix inversion or polynomialexpansion, high-level symbolic processing, as well as many otherpossibilities. A reconfigurable, heterogeneous processing system wouldallow the replacement and regrouping, either physically or logically, ofa mixture of such specific- and general-purpose processing nodes. Theonly requirement is that communications nodes in the electro-optic layerare properly interfaced to processing nodes (modules) in what can betermed the processing layer. The communications layer (opticalinterconnect layer and electro-optical layer) would be consistent infunction across the system and that each processing node (module) have aconsistent interface to the communications layer. In a homogeneous viewof communications, the processing layer is simply an array of processingnodes (modules) that communicate with the EO layer through the opticalinterconnect layer.

Processing Node and Lightnode

The electro-optical portion of a lightnode may be thought of asincluding of a single compound lens structure that spreads out a lightbeam (from a laser, light-emitting diode, etc.) from one or moreemitters and is able to focus light reflected off a mirror or screenonto one or more focal points. Each focal point has a receiver orphoto-sensitive detector for detecting or receiving a light signal froman emitter residing on the same lightnode or elsewhere in the opticalsystem. Thus, a lightnode can defined by a single compound lensstructure that forms an image of all emitters in the system onto asmaller array of receivers plus the associated electronics including theassociated emitters and receivers. In addition to forming an image ofeach emitter in the system, the lens structure contains structure thatspreads out the associated emitter's light (fan-out) so that each partof the system receives a portion of the emitted light (broadcast).

If there are n² emitters in the system under consideration (note changeof notation for convenience only) and each emitter has its own lenselement, then that lens element can focus all n² emitter images onto anarray of n² receivers located in the focal plane of the lens element.The lens structure can be larger than the EO layer only for thoselightnodes not in the interior of the lightnode array. Light at theedges of the node array that escapes collection by the variouslightnodes can be used for off-array communication. FIG. 27 illustratesthe portion of the processing layer associated with a lightnode's EOlayer. Note that this configuration is not uniquely determined by thelightnode geometry. A smaller number of wider processing daughter boardscould span a collection of nodes and be attached thereto by a system ofconnectors or cables.

Referring to FIG. 27, a lightnode 2700 is depicted without the lensstructure, which would be mounted on stand-offs to the right of FIG. 27.A PCB version is depicted including four processing modules 2710 each ofwhich includes four package chips 2720 (e.g., processors, memory, etc.)represented by shaded rectangles. The EO layer is at the right of thefigure with the array of black dots representing the receivers 2730 andthe four open ovals representing the emitters 2740 (e.g., lasers or LEDsor plasma emitters).

Another configuration of the processing layer segmented to match eachnode is shown in FIGS. 28-28B where daughter boards are replaced by thedense packing allowed by MCM techniques. In this embodiment, theprocessing layer associated with the node is located on the back side ofthe EO layer whereas in FIG. 27, the processing layer included fourprocessing modules mounted on daughter PCB cards attached to the back ofthe node's EO layer.

Referring to FIGS. 28A and 28B, a node 2800 is depicted without the lensstructure, which would be mounted on stand-offs above the face shown onthe right. This illustration shows a conceptual rendition of an MCM nodewith the EO layer on a front side 2810 in FIG. 28B and the processornodes on a back side 2820 in FIG. 27. This version illustrates fourprocessor modules 2830 in this single node. The shaded rectangles(representing unpackaged die) in FIG. 28A depict the four processors,each of which may contain multiple processing elements. Memory 2840 isrepresented by the small shaded squares. The shaded squares in FIG. 28Brepresent the circuitry 2850 necessary for transducting electricalsignals for conversion to and from light signals, namely the serdes(serializer-deserializer) elements, as well as the necessarytransimpedance amplifiers, decoding circuitry, and local storage. Thefour open circles represent the four emitters 2860, one serving eachprocessor node. The black dots represent the photo-receivers 2870, onefor each emitter in the system.

The Full Optical Interconnect

A multiprocessing system can be defined to include a number ofindividual processors linked by either electrical or opticalinterconnections, or a combination of the two. Additional linkagesconnect processors to local and/or remote memory. One or more processorscan reside on a single chip or die. Groups of processor chips, alongwith power, random-access and other forms of memory storage, memorycontrol circuitry and other elements form a processor node (module) asdescribed above.

A processor node including packaged chips will typically reside on aseparate PCB that is attached to the EO layer either directly, through aconnector, or through a cable. If the processors are based on bare die,which are much smaller and can be assembled in higher densities thanpackaged chips, processor nodes can be placed on the back side of the EOlayer greatly reducing the volume of the node. The node concept can bethought of as containing multiple general-purpose computing nodesserving as a component of a high-performance computer or supercomputeras well as multiple specific-purpose switching or routing nodes. Inaddition, there are other specific-purpose devices such as messageexamination nodes, encryption and decrypting nodes, processing nodes formathematical functions, etcetera. A combination of these functions,depending on application requirements, is achievable by populatingvarious nodes with different functional processing nodes (modules) arerequired by any particular application.

The Electro-Optical, Optical-Interconnect Cube

A collection of nodes (with their associated lens structures) can bearranged in a square array and support attached or remote processingnodes (modules), form the computing cluster or computing array. A mirroror screen placed above the plane of the lens structure couples the lightemitted from each node to other nodes in the system. The entire assemblyincluding the mirror or screen layer, the array of lens structures, theEO layer and the processing nodes (modules) can be termed a lightcubebecause the shape of the complete system is roughly that of a cube withthe dimensions of the mirror being similar to the dimensions of thearray of EO submodules, and the distance of the mirror from the EO layerbeing close to a side of the array of EO submodules.

An individual lens structure may be mounted on each node or an array oflens structures may be similarly mounted above or beyond a planar arrayof nodes. The electro-optical and optical interconnect portions of alightcube are shown in FIG. 29.

Referring to FIG. 29, a lightcube 2900 is depicted based on a 3 by 3array of nodes 2910 where each lightnode contains four processor nodes(modules). The lightcube can include three layers. On the left is the EOlayer 2920 of 9 nodes 2910. Only the emitters are and receivers areshown. In the PCB version, circuit boards (not shown in FIG. 29),attached to the back of the EO layer, would extend farther to the left.In the MCM version, processing nodes would be mounted directly on theback of the EO layer with signal-conditioning circuitry mounted on thefront as illustrated in FIGS. 28A and 28B. The next layer, slightly tothe right of the EO layer, represents an array of 9 lens structures2930. Each lens structure can include four diverging elements to achievefan-out consistent with the overall image forming geometry. Theseoptical elements are shown as the four small ovals in each lensstructure, for a total of 36, matching the number of emitters in the EOlayer. Each lens structure also contains a large light-collecting andfocusing optic represented by the 9 large shaded ovals. A mirror 2940,shown on the right, comprises the third layer. In this configuration,all three layers lie in parallel planes, with the distance between theplanes constrained by the distance from the far left layer to the mirroron the right, the spacing of receivers in the receiver array, and thetype of focusing optic used.

The lightcube may have processing nodes (modules) attached to the leftof the EO layer, in which case the system is a multiprocessing systemfully interconnected by a FSOI. If connectors to remote communicationsor remote processing elements replace the processing nodes (modules),the lightcube then serves as an electro-optical switch and/or routerhaving full broadcast capability.

Mirror Alignment

Geometrically, by considering the central ray from an emitter in onecorner of the array to a receiver in the other corner, the angulartolerance on the mirror is approximately the receiver spacing divided bythe array diagonal. In practice, the collecting optics considerablyreduce the severity of this constraint. The tolerance on mirroralignment is reduced by the same factor as the optics reducing the imageof the emitter array to the much smaller receiver array size. Thisincrease in tolerance is also given by the ratio of the two conjugatefocal lengths, or, more accurately, the ratio of the size of thereceiver pattern to the emitter pattern. For a node tile of side s, thereceiver pattern fits into a square of about s/2 on a side. The emittersfit into a square that is (2n−1)s/2 on a side. Since the lens structureimages the larger square onto the smaller square, the angular toleranceis increased by 2 n−1 over an unlensed, central ray.

Feedback Control on Mirror Angle

In a typical system represented by FIG. 29, with a receiver array ofabout 30 mm and an emitter spacing of 50 mm, this ratio is 1/5, relaxingthe tolerance on the mirror angle from about 1/20th of a degree to about¼ degree. The absolute mirror tolerance is roughly constant as the arraysize increases since the reduction in size of the emitter image to thereceiver array should be increased. In certain situations, activecontrol of mirror alignment might be required. This can be achieved byadjusting the mirror angle via electro-mechanical positioners derivingtheir control signal from one or more dedicated lasers reflected fromthe mirror itself back onto CCD arrays in the receiver plane might berequired. It is known how to derive an error signal from such anarrangement of a narrow light beam impinging on a photosensitive arrayof small pixels.

Consider a narrow-beam laser mounted at one corner of the EO array and aCCD array in the opposite corner. The error signal is an x-y vector ofpixel deviations from the nominal center of the CCD array. Amicroprocessor containing a table or simple algorithm converts the x-yposition error into three differential drive signals, one sent to eachof three electro-mechanical positioners located on three of the fourcorner mounts supporting the mirror. As the signals are applied to thepositioners, the error signal is reduced. When the correct mirroralignment is achieved, the error signal vanishes, leaving the mirror inits desired position. Should mechanical dimensions change due totemperature or vibration, the error signal will reappear and the mirrorwill be re-aligned.

Receiver Lens Array

By mounting lenses directly over the receivers, for example a smalllenslet array that matches the receiver array, optical alignment becomesless critical. In this case, the main focusing optic would be designedby taking the optical action of this additional lens into consideration.The resulting optical system would be able to focus more of the lightonto a smaller spot aligned with the active area of each receiver.

Optical amplifiers can be placed above each receiver to pre-amplify thelight collected by the lens structure. Thus, the invention can functioneven though the emitted light is too weak to directly excite a receiverelement.

Alternate Embodiments

The array of nodes may be configured in arrangements other than asquare. For example, a linear array of nodes, while not making optimaluse of the light, might be a more suitable configuration for someapplications. For example, an array of 50 by 50 mm nodes in a 2 by 4configuration would measure 100 mm by 200 mm by perhaps 300 mm. Thiswould be a convenient size for portability as a flat package.

The invention can include optics designed to optimize light usage withina given configuration of lightnodes. For example, the light output of anemitter can be confined to a square or rectangular region by usingspecific purpose optics. Such specific purpose optical devices includeprisms, conical lenses, diffractive elements, binary-optical elements,and holographic elements.

The invention can be configured with unfolded optics where the emittersare removed from the EO layer and placed beyond the mirror position(i.e., with at least a portion of the mirror omitted). Two EO layers canthen communicate across a lightcube assembly without a mirror. Even inthe entire mirror is removed the individual EO layers can continue tocommunicate internally electrically, at a local level.

The invention can include the use of mirrors that redirect light intodifferent regions, angles, and directions for communication withreceivers not in the emitter plane. That is, a configuration of nodescan be arranged in other forms than lying in a plane.

The invention can include the use of corner reflectors or corner mirrorsto replace the planar mirror. This concept can be extended to morecomplicated geometric shapes having more than four corners.

The invention can include the use of dichroic mirrors allow multiple useof the light cube space. For instance, 6 EO layers can be connected tothe same cubic volume, where each layer has an associated dichroicmirror that reflects its own associated color. Light from each lightcubewould then occupy the same volume while the different colors would allowthe various lightcubes to operate independently. Three lightcubes canalso use the same lightvolume without dichroic filters.

The invention can include simultaneous, non-blocking broadcast ofinformation. Most interconnect schemes, whether optical or electrical,allow messages and information to be broadcast. However, because of theintrinsic nature of the broadcast techniques and structures disclosedherein, the invention can include broadcast that is simultaneous to allnodes in the system in that the same physical message is distributedsimultaneously throughout the system. It is also important to note thatthe version of broadcast disclosed herein is non-blocking in that amessage being broadcast to all nodes in a system does not block anyother messages from being sent from a different node at the same time asthe given node is broadcasting.

The invention can include wavelength-division multiplexing (WDM) atemitter sites & filters at receiver clumps (clusters). Multiple lasersat different wavelengths (heterogeneous, monolithic laser arrays) can beused at the emitter location in place of single lasers. Since the lensstructure reduces the image of the emitter array onto the receiverarray, each receiver becomes an array of receivers such that themultiple wavelengths from an emitter array are focused onto the receiverarray. The spacing between receivers in this local group can be largerthan the optically reduced spacing of the laser array of thecorresponding emitter. For example, a laser array with spacing of 240 μmin a system with emitters (arrays of lasers) spaced by 40 mm would havethe corresponding receiver with a spacing of perhaps 1 mm between groupsof receivers (a 40-to-1 reduction in image size). If this spacing ratiowere to be maintained between receivers in the local group correspondingto the lasers in an emitter group, a spacing of 240 μm divided by 40, orapproximately 6 μm, would be needed. This small spacing may beimpractical from an optics and electronic circuitry standpoint. Thesolution is to space the receivers corresponding to a given emitterarray of lasers at a physically and electrically reasonable distance(e.g., from approximately 2 microns to approximately 2 mm) and thenfocus the light from the corresponding emitter to illuminate this largerbundle of receivers. Each receiver could then have a dichroic filtermatching the wavelength of the particular laser in the emitter's arrayof lasers. This would ensure that an array of different wavelengthlasers operating within a small region can communicate with an array ofreceivers in a one-to-one manner. Alternative embodiments of theinvention can direct the various wavelengths from the emitting array oflasers onto the appropriate receivers through the use of diffractiveelements (gratings) or dispersive elements (prisms).

The invention can include the use of diffractive lenses and binaryoptics. All techniques of forming images with light or collectingdispersed light or dispersing light may be used with the invention. Forinstance, the invention can include the use of refractive opticalelements (the commonly used lenses), lenses with graded indices ofrefraction (so-called grin lenses), diffractive optical elements such asbinary optics and holograms, light funnels, conical prisms, as well ascollecting mirrors.

Emitter types: plasma, lasers, light-emitting diodes.

All light sources may be used for the emitter as long as they arecapable of being modulated either directly or indirectly. Directmodulation is defined, in the case of a laser, to be that the lasercavity or other intrinsic property is modulated electrically byappropriate circuitry. Indirect modulation is defined to be that anexternal modulation device such as an electro-optical absorber oracoustic-optic modulator is coupled to (e.g., placed above) thelight-emitting element so that light leaving the emitter can bemodulated before it is fanned out to reach the receiving elements.

The invention can include the use of specific purpose elements in thefold-back optics. Specifically, the invention can use prisms ordiverging lens or diffractive optics to shape and expand the emitteroutput so that, after reflection, it illuminates the collecting-lensarray uniformly as possible and with little or no light spilling overthe edges of the collecting-lens array.

The invention can include extending the folded optics in broadcast intoa spill over mode. Specifically, the invention can include adjusting thefold-back optics so that sufficient light from one or more lightnodes isreflected past the collecting-lens array. Any light uncollected andunfocused by the emitting lightcube can then be used to communicate,edge-to-edge, with another lightcube or other device such as i/o devicesor other processing elements.

The invention can include wavefront compensation. When communicating athigh data rates, a wave front correction should be made so that lightarriving at the edge or corner of a lens reaches the intended receiverwithin the same time interval as light passing through the center of thelens. As these geometrical distances are different, arrival times of awave front will be different. A signal of sufficiently short durationwould have its shape spread out in a time longer that the duration ofthe signal. Thus, one signal pulse could be confused for another signalpulse. Such a situation could arise for a system with large lenses orshort signal pulses.

The invention can achieve wave front temporal compensation by includingplacement of a conical refractive element above or below each converginglens in the lens structure. Light travels more slowly in a material withan index of refraction greater than 1 than it does in air (having anindex of refraction only slightly above 1). Typical transparentmaterials (glass, plastics) have indices of refraction between 1.3 and1.9. All of these materials can be configured in a conical shape wherethe material is thicker at the center than at the edges, forcing lighttraveling through the center of the lens to pass through more opticalmaterial than light at the edges, thus compensating for the longergeometrical distance covered by light passing through the edges of thelens. Such a conical element affects the focal properties of the lensstructure and should be taken into account during the design phase ofthe lens structure.

Since the temporal dispersion of the light wavefront grows as the sizeof the lens aperture, another way compensate for such temporaldispersion is to restrict the aperture of the collecting optic. Acompensating increase in emitter power should accompany the loss inlight intensity at a receiver.

The invention can also achieve the same effect by using a flat plate ofoptically graded material where the central portion has a higher indexof refraction that the outer portions. The grading of the index ofrefraction can be continuous to precisely compensate for the timedifferential in wave front arrival. The lens structures themselves maybe made from graded material and the design process would have twocontrol parameters to consider. In addition to the focal properties ofthe lens, the wave front properties should be taken into account duringthe design process.

The invention can include the broadcast of information contained in awavefront or the broadcast of a wavefront itself. A wavefront is anymeasurable physical change in the property of a wave. A wave is aphysical phenomenon that is describable by a wave equation. Examples areacoustic waves (both in bulk and surface) and electromagnetic waves(radio-frequency waves and light). Measurable physical changes may occurin the amplitude, intensity, polarization, phase, and frequency of awave. Any of these properties may be used to carry information byappropriate modulation techniques.

Additional Embodiments of the Invention

The invention can include a general approach to achieving the results ofthe above described optical implementations. These embodiments of theinvention relate generally to the field of fully connected interconnectsfor computer systems and communication systems and/or their subsystemsas well as networks and/or their subsystems. More particularly, theseembodiments relate to a non-blocking, all-to-all, congestion-freeinterconnect for communicating between multi- or parallel processingelements or other devices requiring tight message coupling.

Overview of Method

Let n be the number of endpoints served by the interconnect and k be thenumber of endpoints per physical group or module, where there are mmodules in the system served by the interconnect. Choose n and k suchthat k divides n (not essential, but easier to describe).

A particular preferred embodiment consists of an 8-way, 4-module systemwith k=8 nodes or endpoints in each of the m=4 modules resulting in n=32nodes in the interconnect. Referring to FIG. 30, the four squares 3100labeled “Module #1” through “Module #4” represent the groupings of nodesand receiving stations into physical modules. Circles 3110 represent thefour sets of 8 nodes and each circle is labeled with an index from 1 to32. Each receiving station 3120 is labeled with a number correspondingto its transmitting endpoint node. Thus, circle 3110 with label 1represents a broadcast channel that sends messages to receiving station3120 (small circles) with label 1 in each module 3100 labeled “Module#1” through “Module #4”. It is clear that any convenient grouping oftransmitters and receiving stations can be considered to comprise amodule and that any number of modules can be assembled into a system ofgrouped nodes or endpoints. This modular construction is capable ofsubsuming any number of endpoint nodes and is expandablemodule-by-module. As long as a module contains a sufficiency ofreceiving stations, the expansion can continue until other physicallimits are reached.

In general, a module of the disclosed invention has provisions for nreceivers so that a message from a particular transmitter is received ineach module at a dedicated and corresponding receiver. Thus, a32-endpoint system with 4 modules has 8 transmitters per module and 32receivers per module. The system total is 32 transmitters and 4×32, or128 receivers.

Since a message from a given node, say node 3110 labeled 1 in module3100 labeled “Module #1”, could be destined to any of the 32 nodes 3110in the preferred embodiment, there must be a structure and/or process ofdirecting any message to any or all of its possible destinations. Such astructure and/or process is associated with filtering logic located atreceiving station 3120 in each module. As an example, suppose a messagereaching receiver 3120 labeled 16 in module 3100 labeled “Module #1” ismeant for node 3110 labeled 6. First, note that this message must haveoriginated at node 3110 labeled 16 in module 3100 labeled “Module #2”since destinations labeled 16 can only receive messages fromtransmitters labeled 16. A message need not contain originationinformation as the latter can be added locally in the receiving stationby the logic associated with each receiving station. The packet leavingreceiving station 3120 labeled 16 is potentially passed on to a queueserving each of the 8 nodes in module 3100 labeled “Module #1”. However,decoding logic at the receiving station examines the packet header. Ifthe packet is destined for none of the nodes 3110 in module 3100 labeled“Module #1”, it is simply dropped at the receiving station. If thepacket is destined for only the node 3110 labeled 6, it is routed to thequeue serving that node. If it is destined for a group of nodes withinmodule 3100 labeled “Module #1”, it is sent in parallel to that group ofqueues. In summary, transmitting node 3110 labeled k for 1≦k≦32 sendsits messages to each of the four receiving endpoints 3120 having thesame label k in each of the four modules 3100.

Receivers 3120 represent the second stage of information fan outdiscussed in this disclosure, as will be explained below. Queuesassociated with each node or endpoint 3110 of each module 3100 arephysically and electrically close to the node ports, discussed below,allowing efficient flow-control information to be inserted into messageoutput queues for transmittal to the fabric.

The problem solved by the invention is to efficiently transmit anddirect messages from the input layer to the output layer. There is norouting or path selection occurring at any point in either the inputlayer or the fabric, thus, there are no switches within theinterconnect. Decision logic in the output layer at each receiverprovides a simplified form of routing by opening a normally closed gate,depending on the destination header decoded at the receiver, to one ormore endpoints locally situated in the destination module. There is norouting or path selection required to direct a message to a module sinceany message sent to the fabric arrives at all modules simultaneously.

The input layer, described below, closely follows the usual approach tointerconnect technology; there are differences in the details of thecomplexity of the header added to each frame or flit and similarities inthat buffering and flow control from input buffers back to thetransmitting nodes are used. The fabric layer, also described below indetail, contains no hardware other than a fan-out structure and/orprocess; that is, there are no buffers, no switches, and no routing inthe fabric layer. The output layer, described below in detail, hasapproximately the same complexity as the input layer in that packetbuffering, header decoding, and path gating are all required.

Physical realizations of serial message multiplexing that form the basisof implementing the disclosed invention include the two broad categoriesof (1) physically confined channels and (2) free-space or unconfinedchannels. Physically confined channels may be implemented usingelectrical or RF pulses over wires, differential pairs, shielded cables,circuit-board traces, waveguides, and other structures and/or process.There are also optical implementations of physical channels as fibers,light pipes, and etched channels in conductive or non-conductivematerials. Free-space channels include free-space optical transmissionsas well as RF, microwave, terahertz beams, as well as acoustic beams orpressure waves, which might find application in a mechanical controlsystem.

Fan-out structure and/or process for the various physical channels arebased on the physics of the particular medium consistent withdistributing confined and free-space energy. For example, optical fanout can be effected with lenses, multiple-faceted optical elements,branching light pipes (optical wave guides), diffractive elements,holographic optical elements, photonic structures, and so on. In theelectrical case, the standard multiplexer structure and/or processprovides the fan-out function, as do a set of buffer amplifiers (theoutput channels) excited by a single source (the input channel). In theRF and microwave instances, fan-out is accomplished by standard signalsplitters, wave guides, and other structures and/or process commonlyemployed. In the terahertz realm, fan-out is accomplished by MEMS waveguides and larger-scale photonic structures. Acoustic fan-out isaccomplished by simple channel (physical tube) branching much as in awater-distribution system.

The connectivity achieved by the disclosed method is equivalent to abi-directional, fully connected, non-modular network since every node inthe system can send messages to every other node simultaneously. Whileboth methods (modular and non-modular) scale as n-squared, the practicalreduction in complexity for the modular case is given by the factor 1/k.With k even as small as 8, the reduction in size, power and number ofcomponents can be substantial. Contrast this to a system where k=1.Here, there are 32 transmitters and 1024 receivers. If receivers andtransmitters require about the same amount of space and power, the k=8system will be about 6.6 times smaller and require about 6.6 times lesspower.

A typical interconnect (prior art) is depicted schematically in FIG. 31where inputs 3200 labeled “In 1” through “In n” from n nodes orendpoints are connected to the input layer 3210. This layer typicallycontains buffers and logic to decompose messages into frames or flitsand attach appropriate destination headers to each flit before passingthem on to the fabric layer. The fabric layer 3220 accepts preparedflits from each of the n nodes and distributes said flits according toappended routing information. Output layer 3230 receives the flits,whose headers may be altered by logic in the fabric (prior art), andeffects any necessary buffering, flow control, flit routing, headerremoval, error correction and checking, and flit ordering as may benecessary. Output layer 3230 sends the messages reassembled from flits,stripped of routing information and any error-correction/detection bits,to the endpoints or nodes 3240 labeled “Out 1” through “Out n.”

FIG. 31 represents an “unfolded” block diagram of the interconnect. Thatis, a folding of the diagram about a vertical line through the midpointof fabric layer 3220 would place inputs 3200 adjacent to outputs 3240,more closely representing the physical configuration of an interconnectbetween n nodes, each having an input port and an output port.

FIG. 32 depicts a particular type of layered fabric (prior art) thatexhibits full connection in that every node is connected to every othernode by structure and/or process of one or more “hops” or path segments.Inputs 3300 are the inputs to the fabric (in this example, n is equal to16). Each of the three layers in the illustrated fabric consists of four4-way switches. Each switch, as noted above, necessarily has routing,internal flow control, and buffering (storage queue) as needed. Thefirst fabric layer is at the bottom of the figure and receives inputs3300 from the input layer 3210 of FIG. 31. In FIG. 32, n is equal to 16by way of illustration. Each 4-way switch 3310 in this layer has 4inputs (indicated at the bottom of each box) and 4 outputs at the top ofeach box. The switch outputs 3315 are connected as shown to the inputsof the next (middle) layer of four 4-way switches 3320. The connections3315 between the two layers are arranged so that a flit from any of the16 inputs 300 can be routed to any of the four 4-way switches on thesecond layer. The middle layer comprised of switches 3320 likewise has16 inputs served by the connections 3315. Each 4-way switch 3320 in themiddle layer has 4 inputs (indicated at the bottom of each box) and 4outputs at the top of each box. The connections 3325 between the middlelayer and the top layer are arranged so that a flit from any of the 16inputs of the middle layer can be routed to any of the four 4-wayswitches in the top layer. The top layer comprised of switches 3330likewise has 16 inputs reached by the connections 325. Each 4-way switch3330 in the top layer has 4 inputs (indicated at the bottom of each box)and 4 outputs at the top of each box which are the fabric outputs 3340.

Routing switches in the switch boxes 3310, 3320, and 3330 are indicatedby the 4-way branching 3350, 3355, and 3360 in 4 places in each of the12 switch boxes. As an example, suppose node 1 is to send a flit fromits corresponding position in the input layer 3210 of FIG. 31, which hasdecomposed a message into a sequence of directed flits. The flit inquestion enters input 3300 in the left-most switch box 3310 where it canbe routed by routing switch 3350 to any of the four outputs of thatswitch box. Suppose the destination is for node 12 (output 3340 that istwelfth from the left). There are four possible routes from the firstlayer to switch boxes 3320 in the second layer via those connections3315 that leave the left most switch box 3310. Suppose a particular pathhas been selected by the routing mechanism or algorithm directing theflit to the third switch box 3320 from the left. The flit then has onlyone choice to reach output 3340 (12^(th) from the left), namely it mustpass through the middle layer switch box 3320, third from the left, tothe top layer switch box 3330, third from the left. This situation isindicated by the bold-marked pathway 3351.

Suppose that another flit is using exit port 3361 in the top layer(there are four paths leading to this port and any one may be used atany time). The flit of interest must then be delayed (temporarily storedin a queue) at port 3361. If the flit queue at port 3361 is full becauseof multiple flits attempting to access that port, the flit of interestis either discarded and later retransmitted, or a flow-control messagemust be sent back through the fabric requesting that the flit ofinterest be temporarily stored at an exit or entrance port or fan-outlocation in a lower layer.

A more serious situation develops when port 3356 in the middle layer isoccupied with traffic prior to the flit from input 3300 at the far leftbeing injected into the fabric. Alleviating congestion at such a port3356 can slow down any traffic flowing through such a port 3356.However, there are three other routes through the middle layer; boldpath 3352 represents one of the alternate routes. A global-flowalgorithm could manage such a situation and keep messages flowing at anoptimal rate (reduced by the algorithm routing and storage delays).On-the-fly re-routing can also be used where an alternate path is chosenonce the congestion is noted presuming local storage is not available.That is, the flit must “back up” one layer and select another route. Ofcourse, the same situation can occur on the new route. In addition, theflit can now be the cause of other flits being delayed or seekingalternate routes. In this way, congestion can back up into allswitch-box exit ports below or at the level of the original port 3356.If this happens, the global situation must be detected and all traffichalted until the fabric congestion dissipates by all queues emptyingaccording to their normal operating structure and/or process.

Flit queuing, detection of congestion, and switch routing all requirespecific hardware within the fabric and efficient algorithms to managecongestion any time such congestion arises. In fabrics serving a fewtens of nodes or more, the type of algorithm employed may well depend onthe details of the traffic and, hence, on the particular applicationsbeing run on the computing nodes. Adaptive control algorithms provide apartial solution to this particular problem. Often the expense of theadditional in-fabric hardware and maintaining the software required fortraffic management can prove to be a significant fraction of theinstallation cost.

FIG. 32 represents an “unfolded” block diagram of a layered fabric. Thatis, a folding of the diagram about a horizontal line through themidpoint of fabric layer 3330 would place inputs 3300 adjacent tooutputs 3340, more closely representing the physical configuration of afabric fully interconnecting n nodes, where each node has an input portand an output port.

The invention can include apparatus for effecting a non-blocking,all-to-all, congestion-free interconnect for communicating betweenmulti- or parallel-processing elements or other devices requiringmessage coupling. Each endpoint has an associated input serial-datachannel that is shared among multiple endpoints in the output layer.Each endpoint contains decoding logic and data-storage buffers. Thisapproach eliminates congestion spreading while retaining the advantagesof an all-to-all fabric. The resulting interconnect is equivalent to aone-hop, n-squared, fully connected fabric with endpoint-localdistribution.

The invention can include methods of broadcasting messages over multipleserial data channels wherein each serial data channel originates at asingle node or endpoint. Each serial channel then delivers said messagesto a plurality of nodes or endpoints by branching in a manner consistentwith the physics of the information carrier (e.g., light, RF energy,electrical pulses). In this manner, a single serial data channel isshared among multiple receiving endpoints where each endpoint containsdecoding logic as well as data-storage queues and routing logic toeffect desired distribution of the received messages. The invention canemulate a virtual, circuit-switched network, but directly supports aparticularly simple version of packet switching without routing in thedistribution fabric.

Past approaches to a fully connected network of n nodes have used n²transmitters and n² receivers. The modular approach (or endpointgrouping) used in the present invention reduces the required number oftransmitters of such a network by a factor of n (to n) and the number ofreceivers by n/m (to n×m), where m is the number of modules or physicalgroups. Each modular grouping consists of n/m transmitters and nreceivers and the modules are of a convenient physical size thatelectrical interconnections between components comprising a physicalgroup or module are simple to engineer and have paths short compared tothe total interconnect latency.

The network uses a packet-directive scheme wherein flits have only adestination header. This scheme is to be contrasted with routingmethods. The disclosed interconnect does not require that routinginformation be added to packets; in particular, multi-layer routinginformation is absent. The destination header is only used after themessage has traversed the fabric to the output layer; there is noin-fabric routing or destination routing required or used in the presentinvention. Instead, each serial channel branches locally within orbefore the destination module with a multiplicity equal to the number ofendpoints in the module. At the end of each branch of each serialchannel, packets are locally distributed to endpoints within the moduleas indicated by the destination header.

At the heart of the invention is a single serial data channel that maybe shared among multiple endpoints. Each endpoint contains decodinglogic and data-storage queues. The serial data channel has many possibleembodiments in that the concept supports and is consistent with anystructure and/or process of physical channel and is valid for free-spaceoptical channels, electrical channels, fiber and light-pipe channels aswell as any other structure and/or process of transmitting and receivinginformation over a communications channel, such as RF and microwave.

The resulting fabric allows efficient flow control, both at theinput-layer and output layer since the modular input layer is closelycoupled (electrically or by other structure and/or process) with theoutput layer. In the disclosed invention, flow control is an interactiontaking place between local partitions or modular groupings of the outputand input layers, which are physically adjacent within a module. Such aninterconnect is one hop with no switches, queues, routing, and flowcontrol within the fabric and the modular concept allows inputs andoutputs to be physically close, global control is not required.Flow-control issues are detected locally, within a module, and aflow-control message is sent to the fabric and broadcast to all nodes,where local action can be taken as necessary. In addition, locks,barriers, tags, and real-time clock synchronization are all possible torealize in an efficient manner within the fabric, making possible areal-time, transaction-based, multiprocessing system.

Conflicts can occur only at the endpoints and are managed by flowcontrol and message queuing. There is no allocation of receiver cycles,which would require a completely synchronous system. The standard methodof receiver sharing is essentially a TDMA approach demanding some sortof global control and control data structures, which are simply notrequired in the present invention.

Congestion spreading into or within the fabric cannot occur because (1)there are no switching branches in the fabric to be blocked and (2) aflit cannot be blocked from being queued.

An interconnect built in the described fashion overcomes all of theproblems listed above. That is, the invention discloses a structureand/or process of obtaining a congestion-free interconnect that directlysupports, by its architecture, broadcast, multicast, and all-to-allmessage passing without the use of global flow control. In addition,efficient and effective conflict resolution is enabled by the modularityand flow-control information local to each module. Multicast is thenative message-passing mode of the disclosed interconnect; that is, amulticast transmission is equivalent, in its simplicity, to apoint-to-point transmission.

Referring to FIG. 33, the input layer consists of n channels forconverting parallel messages into serial flit streams. Input 3400 fromnodes labeled “In 1” through “In n” send a message, typically over aparallel data bus, to a FIFO (first-in-first-out queue or buffer) 3410for temporary storage. Destination information as well as otherinformation such as message length, process origin, message type isreceived by the control 3420, which both segments the message into flitsand passes data a flit at a time from message queue 3410 to flit queue3430. Control 3420 also constructs a header for each flit and any otherflit-dependent information such as parity or CRC (cycle redundancycheck) bits for downstream checking and verification of flit integrity.Control 3420 then allows the “bare” flit to pass to queue 3430 where theheader and CRC information are added by auxiliary line 3440. Control3420 also monitors the state of queue 3410 and is able to alert the nodeby line 3450 of any potential buffer overruns, serving as an input-layerflow control. A fully prepared flit with appropriate destination header,CRC check, and other desired information then passes to serializer 3460where it is 8 bit/10 bit-encoded (if desired) before passing into thefabric as a sequence of individual serial pulses through port 3470.

Flow control information from the output nodes corresponding to theinput nodes 3400 is presented to control 3420 by connection 3480. In thepreferred modular embodiment illustrated in FIG. 30, each networkendpoint 3110 contains a message queue 3410 for out-going messages and aflit queue 3430. Flow control information from the output queue(discussed below), can be inserted at the front of the flit queue 3430for immediate or next-flit presentation to the fabric. That is, theflow-control mechanism allowed by the disclosed invention makes directuse of the fabric, ensuring that no extra-fabric structures arerequired.

A particular innovation of the present invention is that flow-controlinformation represented by lines 3450 (to the transmitting node) and3480 (from any receiving station associated by routing information atthe receiving end to the transmitting node in question) is eitherentirely local in nature by being associated with the same node or issent out over the fabric by control 3420. This innovation will bediscussed in greater detail below.

The invention can include a branching multicast channel, therebyenabling a multicast native operating mode. FIG. 34A depicts a singlemulticast channel, of which n such channels comprise the fabric layer.Said channel is the primary focus of the present invention. Each input3500 to each multicast channel represents a serial stream of encodedbits (the prepared flits from output 3470 of FIG. 33). This serialstream, in the preferred embodiment, typically consists of, but is notlimited to, electrical pulses. This is conventional, since the output ofthe computing endpoints or nodes, as well as the entire input layerdepicted in FIG. 33, are typically high-speed electrical devices whereinformation is encoded in serial and parallel electrical signals such asfound in present-day electronic processing systems.

The stream 3500 of electrical signals is presented to gateway device3510. In an electrical-only embodiment, as typically found in mostinterconnects in use today, device 3510 would be a driving or bufferamplifier that suitably matches the impedance of the source stream 3500to the physical characteristics of the communications channel 3520,allowing gain as required to boost the power level for servicingmultiple endpoints. In the optical case, communications channel 3520 maybe realized as any of several physical structure and/or process.Included, but not limited to such structure and/or process are thefree-space optical methods as well as fiber-bundle channels consistingof one or more optical fibers or optical light pipes that confine theoptical signals. Other forms of energy transfer, such as microwave,terahertz wave, as well as standard RF-band energy (from kilohertz togigahertz) will be recognized as being viable forms that are subsumed bythis disclosure. A valid reason for using RF-channel transmission wouldbe that the various modulation techniques as disclosed in U.S. Pat. No.7,136,419 entitled Pulse width communications using precision timing,the entire contents of which are hereby incorporated by reference hereinfor all purposes, as well as standard modulation techniques such asamplitude, phase, and frequency modulation as well as the variousspread-spectrum techniques may be used to achieve increased channelbandwidth beyond that of the prevalent pulse amplitude modulation (PAM)encoding.

Channel 3520 branches by fan-out structure and/or process 3530 into aplurality m of channels 3540, one of each channel 3540 is directedtowards one of the m modules 3100 of FIG. 30. In the preferred opticalembodiment, fan-out structure and/or process 3530 is a spreading lensfabricated such that all modules are illuminated or faceted distributinglenses directing a portion of the light to each module. In theelectrical case, device 3530 is a standard fan-out component, typicallya multiplexer. In the RF, microwave, or terahertz case, device 3530 is asplitter of suitable design for the particular frequency beingmultiplexed (an example is the TV-signal splitters often found in homeshaving more than one device requiring a TV signal). Returning to theoptical case of the preferred embodiment, device 3530 can be implementedby any optical device capable of splitting a beam of light into multiplebeams. Devices commonly used for such optical multiplexing arediffractive elements, holographic optical elements, and beam splitters.Another way of effecting fan-out device 3530 in the optical embodimentis the use of a fiber bundle for channel 3520. The fiber bundle is thensubdivided into m smaller bundles, producing the desired distribution ofa single optical channel to m secondary channels. It is clear that thenumber m of branches 3540 is not restricted to 4 as was chosen forpreferred embodiment. Any convenient number greater than or equal to 1produces a functional interconnect. As the number of nodes n increases,it becomes impractical from an electrical or board- or chip-levelstandpoint to increase the number k of nodes per module beyond somesmall integer such as 8 or 16. This implies that an increasing number ofnodes n must be accommodated by an increasing number of modules m.

The invention can include a passive fan-out device. It is one of theprinciple innovations of the present invention that such division orsplitting of channel 3520 by fan-out device 3530 into m multiplechannels 3540 contains no switches, no queuing or buffering, nodirection or routing specification or hardware, and no flow control. Inthe preferred embodiment, device 3530 is completely passive in thatrespect. It may be seen, however, that the disclosed channel splittingis consistent with control of device 3530 by electrical signals oroptical signals to effect dynamic alterations in the function of fan-outdevice 3530 nor does the present disclosure limit the operation to apurely passive device.

The invention can include local connectivity within modules or groups.It is another principle innovation of the present invention that thebranching into m channels is directed towards the m modules or localgroups of endpoints. A cost advantage of this grouping was explainedabove. A key advantage of this grouping is that flow control no longerneeds to be global in nature since the components in each module areelectrically close to each other. Nodes grouped in a module cancommunicate between themselves, as needed, electrically with low latencyand minimal congestion. Nodes in other modules communicate exclusivelyvia the fabric. Nodes within a module typically communicate via thefabric also, but the possibility of extra-fabric communication ispresent and is available for either increased in-module bandwidth andcommunication channels other than to the fabric (for example, to supportexternal I/O devices).

Sub channels 3540 labeled “Sub Channel 1” through “Sub Channel m” eachcontain the same information as in the main channel 3520. Each subchannel 3540 is directed towards a module 3100 of FIG. 30 labeled“Module #1” through “Module #4” in the depicted preferred embodiment.Each module has device or receiving station 3550 for each of the n subchannels directed to that module. In the preferred embodiment, receivingstations 3550 comprise photo detectors, trans-impedance amplifiers, andmultiplexers mounted on the same plane and near to the gateway 3510containing lasers or light sources. In an electrical embodiment, thereceiving station 3550 consists of a buffer amplifier to drive themultiplexer. The multiplexer in receiving station 3550 furthersubdivides the channel into k additional sub channels 3560. Informationflows from receiving stations 3550 to the m×k output channels 3560labeled {1,1} through {1, k} for group 1 and {m, 1} through {m, k} forgroup m, where each set of labels {i,j} for 1≦j≦k indicates connectionsresiding in or directed towards module i, depending on the particularphysical implementation.

Each of the n multicast channels, one of which is depicted in FIG. 34A,effects a 1×m×k fan-out separated into m groups of k end channels in agroup. In the preferred embodiment where n=32, k=8, and m=4, eachmulticast channel provides a 8×4=32 way, parallel splitting of the datastream, where each of the 32 sub channels carries the same informationas the original channel.

Fan-out device 3530 can be configured to produce a continuous branching(beam spreading). In the optical embodiment, a negative lens or adirecting wedge can be used as taught in disclosure A or a wide-beamantenna in the RF, microwave, or terahertz realizations. Devices 3530may also be carrier-conversion devices such as optical-to-electrical,electrical-to-optical, or any combinations thereof and still maintainthe purpose and function of the disclosed invention. Likewise,connections 3540 and 3560 between conversion devices 3530 and 3550 neednot support the same form of physical carrier.

In the optical embodiment, devices 3530 and 3550 may support or containoptical-gain structure and/or process (optical amplifier such aserbium-doped glass or a powered optical-electrical-optical conversiondevices). This would allow the information to be subdivided into manysub channels without requiring a single powerful laser or light sourcein device 3510. This is the optical equivalent to placing boosteramplifiers in an all-electrical fabric. The importance of incorporatingoptical amplifiers or buffer amplifiers in the fan-out or splittingstructure and/or process 3530 is that the multicast fabric disclosedherein is scalable to a large number of nodes or endpoints, far beyondthe example of n=32 used of the preferred embodiment.

The invention can include an interconnect between n and N endpointswhere N>n, It is clear to see that channel branching depicted in FIG.34A is not limited to a single branching layer to the m modules.Multiple fan-out devices 3530 placed at ends of channels 3540 and beforedevices 3550 can further multiply the number of channels as requiredsupposing need for multiple output layers 3230 of FIG. 31. A usefulexample would be where multiple output layers required information fromthe same input layer 3210. The resulting interconnect would no longer bea symmetric n×n device but, rather, an n×p device, where p is somemultiple of n.

The invention can includes the use of alternative carriers; beyondelectrical and light. The multicast fabric of FIG. 34A is generic in thesense that it supports many different physical communication approaches(light, radio waves, microwaves, terahertz waves, even acoustic waves).A particular optical embodiment has been presented, but that in no waylimits the generic innovation of a multicast channel that branches intosub channels, each directed toward a module or local grouping ofendpoints. Each particular implementation based on a particular anduseful physical communication channel has the same properties of noin-fabric storage, no in-fabric routing or packet direction, noin-fabric flow control, and no need of global control of the messagetraffic as a whole.

The branching channel depicted in FIG. 34A contains no buffer orswitches. This simple fact eliminates congestion spreading. Each of then channels comprising the fabric has an input and a m-way branch orfan-out, where m is the number of modules in the system. Each of the mbranches serve a single module. Each of the n branches to each modulefan out a second time into k paths for a total of n×k possible paths toeach module. The total number of paths is then m×n×k=n² showing that thefabric effects a fully connected, n×n system.

It is obvious that one could run multiple groups of serial channelsshown in FIG. 34A in parallel effecting a parallel n-way interconnectfrom multiple serial interconnects. For example, paralleling 8 or 10(for data and control) channels, the interconnect would have 8 times thebandwidth. Attention must be paid, using well-known techniques, to anypossible skewing between the parallel bits comprising a byte sent acrosssuch an interconnect.

Preferred optical embodiments of 3510, 3530, and 3550 of FIG. 34A areshown in FIGS. 34B, 34C, and 34D. Referring to FIG. 34B, upper panel,serial input stream 3500 enters serializer 3511, a commonly availableelectronic device for converting a parallel data word into a serialstream of digital pulses, where it emerges as a serial data stream. Thisserial data stream provides the input for laser-driver amplifier 3512,which supplies the necessary current for modulating the intensity oflaser diode 3513, suitably biased as shown. The resulting beam ofmodulated 3514 light is focused by beam-adjustment lens 3515, ifrequired. For example, the beam shape emanating from an edge-emitting,semiconductor laser typically has an elliptical rather than circularcross section. A suitable aspheric lens 3515 can be used to both obtaina more desirable cross section and the required beam-spread angle forilluminating an optical element in the next stage 3530 of FIG. 34A. Thefocused, modulated beam is an embodiment of channel 3520.

The lower panel of FIG. 34B illustrates an alternative embodiment basedon external modulation. Here, serial input stream 3500 enters serializer3511 as above. This serial data stream provides the input for driveramplifier 3516, which supplies the necessary voltage for controlling theexternal modulation device. Light source 3517, typically a diode laseror light-emitting diode operating in the continuous-wave (CW) modeproduces a continuous beam of light 3518, which is modulated by externalmodulation device 3519, producing an intensity- or pulse-modulated beam3520. Device 3519 may be any of the typically used intensity modulatorsthat are sufficiently fast for the purposes envisioned by the invention.Examples of device 3519 are electro-optic modulators (organic filmpolymers, lithium niobate crystals) and acousto-optical modulators orBragg cells (a piezo-electric transducer exciting mechanical vibrationsin an optical medium such as glass).

The invention can include in-fabric light amplification for handlingmore endpoints. FIG. 34C illustrates the preferred optical embodiment offan out 3530 of FIG. 34A. Cone of light 3531, possibly focused by lens3515 mounted with laser diode 3513 of FIG. 34B, illuminates opticalelement 3532 which splits the light into m distinct beams 3533 orspreads out the light so that it can illuminate an appropriately widefield containing lenses 3534. The beams 3533, or alternatively the widelight field, illuminate optical elements 3534 which direct and focus, asnecessary, light onto optical amplifiers 3535. Excitation structureand/or process 3536 provides the necessary energy for amplification ofbeam 3533. Amplified light exits optical amplifiers 3535 and is focusedby lenses 3537 into the Sub Channels 3540 of FIG. 34A.

Erbium-doped glass is one way of effecting optical amplifiers 3535;another way is a resonant-cavity optical amplifier based on anelectrically pumped semiconductor enclosed in a Fabry-Perotinterferometer; another way of effecting device 3535 is by an opticalparametric amplifier; yet another way is provided by Raman amplificationmaking use of a nonlinear interaction between the signal 3533 andemission from a pump laser within an optical fiber. Yet another methodmakes use of the vertical-cavity, semiconductor optical amplifier; thisdevice also requires a resonant cavity with high-reflectivity mirrors toachieve useful optical gain. Each of these devices requires eitherelectrical excitation or optical excitation, indicated by structureand/or process 3536 in the figure. FIG. 34C shows a schematicillustration of pumping or excitation 3536 of the entire set of opticalamplifying devices comprising the amplification-fan-out structure and/orprocess of device 3530 of FIG. 34A.

FIG. 34D illustrates the preferred optical embodiment of receivingstation 3550 of FIG. 34A. Sub channel 3540 labeled with index j where1≦j≦m represents a beam of light from fan-out 3530 of FIG. 34A. Thelight is detected by photodiode 3551 and the resulting electrical pulseis input to trans-impedance amplifier 3552. The amplified signal is thensent to limiting amplifier 3554 for pulse shaping and limiting andthence to clock-and-data recovery device CDR 3555 for phase adjustmentto ensure coherence with the clock signal in the receiving station. CDR3555 typically includes a phase-locked loop or PLL. The recovered andshaped signal then passes to deserializer 3556 where the serial streamof pulses is converted into a parallel data word or byte. The paralleldata word then is sent to multiplexer 3557 where it is fanned out to thek outputs 3560, labeled (j, 1) through (j, k).

Each of the three views of FIGS. 35A, 35B and 35C depict a mapping of ninput channels to n×m×k output channels, illustrating the fullyconnected, switchless fabric in a purely conceptual manner. FIG. 35Aillustrates the fabric in as a 3D configuration. There are n inputchannels 3600 to the n×m×k interconnect fabric 3610. The outputs offabric 3610 are grouped into m groups forming an output row 3620. Ineach group in output row 3620, there are k outputs for a total of m×koutputs in each row 3620. These n outputs 3620 provide n inputs to theinterconnect output layer discussed below. FIG. 35B is a side view ofthe switchless fabric layer with n inputs 3600 to the fabric 3610branching out to n connection bundles 3630 where each bundle contains mgroups (one for each module) of k channels each. FIG. 35C is a top viewof the switchless fabric layer 3610 with inputs 3600 representing astack of n inputs depicted in FIG. 35A. There are m output bundles 3640where each is n channels deep and each contains k serial lines.

FIGS. 35A-35C are conceptual, depicting an n×m×k fabric in threedifferent views. Each of the input channels 3600 and its internalbranchings (not shown) within fabric layer 3610 is realized by themulticast channel depicted in FIG. 34A. That is, the block labeled 3610contains n multicast channels described by call outs 3500 through 3560of FIG. 34A. The purpose of FIGS. 35A-35C is to explicitly display thefan-out from n to n×m and thence to n×m×k serial channels.

Referring to FIG. 36A, the function of output layer belonging to modulej is shown with module 1 through m indicated by dots. Inputs 3700 in ksets of n inputs in each set provide n×k inputs to each of the mmodules. Each group of n inputs 3700 enter control 3710, which convertsthe serial inputs to parallel words and then assembles words into flits,finally arbitrating and distributing flits, according to destination. Ifa serial stream entering control 3710 is meant for an endpoint servicedby the particular module control 3710, that flit is allowed to exitcontrol 3710 by line 3720 and be queued for delivery to the targetedendpoint in queue 3740. Data sent to queue 3740 are monitored by thearbiter in control 3710 and flow-control information is sent over line3730 as described below. Queue 3740 sends either flits or completere-assembled messages, depending on the precise internal function chosenfor control 3710, to target endpoints over outputs 3750.

Connections 3730 of FIGS. 36A-36B are made to connections 3480 of FIG.33 locally, within each module, to provide the basis for a flow controlallowing control 3710 of FIGS. 36A-36B to broadcast a control messagethrough the fabric by control 3420 of FIG. 33 located physicallyadjacent to and logically grouped with queue control 3710 of FIGS.36A-36B.

The invention can include local flow control distributed back thru thefabric, thereby obviating the need for global flow control. Referring toFIG. 36B, a particular instance of control 3710 of FIG. 36A is shown ascomprising, in the preferred embodiment, a set of n deserializers 3711,which convert the serial data streams from the fabric to parallel datawords. Discriminators 3713 decode destination headers and senddestination information to the arbiter 3714. Meanwhile, the paralleldata are temporarily stored in queues 3712, for example, to assemble acomplete flit composed of multiple data words. The arbiter 3714 controlsthe k multiplexers 3715 as to which flits are accepted by which of the kmultiplexers 3715, which then allow flits to pass along output lines3720 to the queue 3740 of FIG. 36A. If there is potential contention dueto multiple flits being directed from inputs 3700 to a particularcontrol 3710 in such a manner as to overload a particular queue 3740 ofFIG. 36A, arbiter 3714 is designed to detect this potential overloadcondition and notify the sending node over line 3730 to stoptransmission until danger of contention has been relieved by theemptying of queue 3740 of FIG. 36A. Note that such flow control preventsqueue 3712, internal to control 3710, from overflowing as subsequentmessages over the input channel in question will be halted by the flowcontrol over line 3730 propagating through the fabric to any sendingnodes as described above.

Advantages flow from the combination of the two key ideas of (1)modularity or grouping of endpoints or nodes, and (2) switchless channelbranching or fan-out. The modularity concept allows local flow controlwith efficient back flow through the fabric while switchless channelbranching ensures that the native mode of operation is multicast. Thisfact implies that the one-to-all mode is essentially the same as thepoint-to-point mode. This equivalence is a primary distinction betweenthe present invention and previous implementations of computerinterconnects.

Combining the two key ideas allows the last fan-out stage to take placewithin a module of k nodes rather than over the entire set of n nodes.Thus, the module sizes stays constant even as the number of nodesincreases (at least up to some limit depending on the layout of theend-stage circuits as shown in FIGS. 36A-36B). The last-stage fan-out ofFIGS. 36A-36B then grows as n rather than n² and can easily be handledelectrically using standard printed-circuit-board techniques even for areasonably large n. That is, the final multiplicity of paths are localand straightforward to fabricate using standard printed-circuit-boardtechniques and practices. A practical result of the combination is theelimination of the need for a multilayer interconnect with attendantin-fabric switching, global flow control, message queuing, and hardwarerouting. This elimination of in-fabric control and hardware is anotherkey distinction between the present invention and other implementationsof computer interconnects.

The invention disclosed herein provides a way of completely eliminatingcongestion spreading while, at the same time, allowing traffic betweenall system endpoints simultaneously (all-to-all communication) as wellas point-to-point and multi-cast communication. The message latency inthe disclosed interconnect is the same for multicast (one-to-all) as itis for point-to-point and the latter is at least as efficient in thedisclosed invention as it is for presently available, commercialinterconnects. The invention provides a non-blocking, all-to-all,congestion-free interconnect for communicating between multi- orparallel processing elements or other devices requiring messagecoupling.

The potential for contention of access by simultaneous messages or flitsat any given endpoint means that some sort of queuing, at minimum, mustbe done in the output layer. That is, all systems that deal withcontention must have queues in the output layer. In previousinterconnect implementations, flow control originates in the outputlayer as well as in each stage of the fabric (the presence of a storagebuffer is typically accompanied by flow-control logic). In contrast, thepresent invention requires only endpoint-local flow control to addressthe contention problem.

It will be appreciated by those familiar with the operation of computerinterconnects that the present invention simplifies the employing locksor barriers (barrier synchronization), transaction tags, and clocksynchronization. Furthermore, the operations of scatter (a one-to-manymode where one node sends different messages to different members of aworking group), gather (the inverse of scatter), and the variants on thereduction operation are all greatly simplified and performance enhancedby the present invention.

Further Additional Embodiments of the Invention

A properly designed optical system ensures that adequate intensity fromany emitter reach its corresponding photo-detector (one in each module)and that any other photo-detector, other than the intended one,receivers negligible light from that emitter. The goal is to ensuresufficient signal strength at a receiver, resulting in a low bit-errorrate and minimizing cross talk between optical channels.

Embodiments of the invention relate to optical design of free-spaceoptical interconnects that include efficient methods of optical fan-outand a closely related method of optical demultiplexing of the combinedand merged fanned-out light beams. More narrowly, the invention relatesto methods of efficient light distribution and collection within anoptical system. This is to be contrasted to the more usual goals of anoptical system wherein effort is taken to produce high-quality images.While the system disclosed herein does produce images, their quality isof secondary importance to the efficiency of light collection.

Wide Angle Lens and Optical Distortions

Using simple optics with single-element lenses for the collecting opticsand simple negative lenses for the broadcast optics leads to afunctional FSOI (free space optical interconnect). However, the array ofemitters typically spans an area of many times the area of a module'sreceiver array. When the mirror distance, or, equivalently, halfdistance to the focal plane, is constrained to be approximately lessthan or equal to the linear size of the emitter array, a situationcalling for a wide-angle lens results. Using simple lenses, whetherspherical or aspheric in design, precludes achieving a flat focal fieldwhere the receiver grid is a reduced and registered image of the regularemitter grid. (Regularity of the emitter grid is demanded by a systemincluding interchangeable modules.) A compromise is reached in theoptical design (broadcast lenses, mirror, and collecting lenses) wherethe size of the focal spots, their precise locations, and theintensities at each receiver on a regular receiver grid are varied toachieve an overall best quality of image location, spot size, andreceiver intensity. The criterion for this optimum is the lowestpossible bit-error rate given a particular emitter power and receiversensitivity. Thus, efficiency of light collection is paramount.

Practical design of the collecting lenses requires that the numericalapertures (on the side toward the receiver arrays) be held to reasonablevalues, essentially much less than 1. Equivalently, the f/stop of thecollecting lenses should be kept at reasonable values, perhaps above 2.Violating these conditions greatly increases the distortions in theimage of the emitter grid, implying poor registration with the array ofreceivers, as well as shape distortions in individual receiver spots orilluminated regions. This later distortion results in a waste of lightenergy.

Correcting Distortions

Since a portion of the noted distortions fall into the class ofspherical aberrations, typically observed in uncorrected wide-anglelenses, or are of the classic coma distortion of a point source imagedwith an off-axis focusing lens, the usual methods of image correctioncan be applied. However, such corrections typically involvemultiple-element lenses that are both difficult to design and expensiveto fabricate. An alternate method of overcoming distortions then becomesdesirable.

Inefficient Light Distribution

A collecting lens with a small numerical aperture typically has a smalldiameter relative to the distance to the receiver array. This impliesthat the area of the collecting lens is typically considerably less thanthe area of the module being illuminated by an emitter. In a module witheight emitters, there are eight broadcast lenses and one collectinglens. Considerations of beam divergence from the emitters and the notedrestrictions on apertures of the collectors implies that the ratio ofthe area of a collector to the area of the face of a module is much lessthan 1. Typically, a collecting lens receives only a few percent of thelight from each emitter, again underscoring the need for efficient lightcollection.

In a simple distribution system, each collector is illuminated by a widebeam of light spreading out from each broadcast lens. The focused imagesof the emitters may be highly distorted, as noted above, and the focalpattern may be poorly registered with the receiver grid. Poorregistration means that the optical system has low tolerance toalignment errors, poor resistance to effects of mechanical vibrations,and a performance restricted to a small temperature range, astemperature variations may result in differential expansion of systemcomponents.

Mirror Distance and Optical Distortions

The distance to the mirror can be shortened by increasing the (negative)power of the broadcast lenses and tilting them slightly to direct thebroadcast beams to achieve uniform coverage of the array of collectinglenses. This shortened distance increases the distortions above.Increasing the distance to the mirror eventually reaches a point wherethe broadcast optics have no focusing properties; beyond this point, thecurvatures of the broadcast lenses become positive. This point dependson the natural divergence of the emitter beams. The result of thismirror-distance increase is to decrease the size of each receiver arrayand increase the size of the optical system. Each of these results maybe undesirable in a particular realization where the receiver spacingmight become too small to be practical or the mirror distance too largefor a particular application. Accordingly, a means is desired to keepboth the receiver spacing and the mirror distance within particulardesign regions that are application dependent and constrained by othercomponents in the system.

More Modules Mean More Power

Additionally, as more modules are incorporated into a given realization,the emitter power must increase as the number of modules increases. Thisis simply because each emitter must illuminate additional modules whileensuring that each receiver have adequate light intensity for low-errorcommunications over the optical channels established by theemitter-receiver optical paths.

Solution to These Problems

To overcome the problems of (1) requiring high-powered light sources,(2) distortions in the focal plane, (3) image size at the receiver, and(4) an unwieldy optical region, a more careful design of the system ofbroadcast and collecting lenses is necessary. If each broadcast lensdirects light from its emitter to the collecting lens above each moduleso that no light falls on any other portion of the system, then theemitter power can be reduced by a factor of approximately 15 in afour-module system and by a factor of 33 in a 16-module system over thatrequired by a simple distribution method.

Collecting-lens design depends critically on the precise manner in whichthe broadcast lens distributes light in the system. In addition, thecollecting lens determines the magnification of the optical system andhence the image size, which is the size of the receiver array. There aretwo types of collecting lenses that might arise in any given design,namely (1) a simple lens including a single curved surface such as aplano-convex lens and (2) a compound lens including two or more curvedsurfaces such as a bi-convex lens (two positive surfaces) or a meniscuslens (one positive and one negative surface). In addition, one might usetwo separate lenses, such as two Fresnel lens spaced a certain distanceapart to accomplish the same result.

A simple distribution system that merely allows emitter beams to spreadout unimpeded will generally require a more complex collecting lens,both to collect adequate light and reduce inherent optical distortions.Typical complications include use of multi-element aspheric elementswith possible anamorphic surfaces. A complex distribution systeminvolving precise direction of light onto particular targeted collectinglenses typically results in a simple plano-convex collecting lens with aspherical or parabolic surface.

The present invention involves designing broadcast lenses particular totheir location with respect to the emitters. Furthermore, once theparameters of the broadcast lenses are selected, the collecting lensesabove each module must be designed to accommodate the distribution oflight from the several broadcast lenses in the system and focus thepattern of light reaching each collecting lens onto the set of receiversbelow that lens.

To accomplish these goals, the broadcast lens is divided into a numberof facets equal to the number of modules in the system, or one less thanthis number if it is desired that a module not communicate with itselfoptically. In general, each facet includes a segment of a lens ofcurvature (power), diameter, and center location particular to thatfacet. The associated emitter then illuminates the set of facets inroughly equal proportion. Each facet then directs its received lightonto a different collecting lens. In this way, the light from an emitteris efficiently used, with very little light wasted in illuminatingnon-functional parts of the optical system.

Once the broadcast lenses are chosen, the collecting lenses must bedesigned to achieve the desired system dimensions (mirror spacing andsize of the receiver array or receiver spacing). A further innovation ofthe invention allows a system magnification (image size) other than theone inherent in the system geometry as defined by the module size andspacing, the number of receivers per module, the distance to the focalplane, the distance from the emitters to the lens array and the distanceof the lens array to the mirror. Particular embodiments of thecollecting optic include a split lens as well dual offset lenses. In thesimplest case, the collector is a plano-convex optic, possibly in aFresnel implementation. Simplicity in this optic is made possible by thefaceted broadcast lenses.

An added benefit of so restricting the distribution of light from eachemitter is that the collecting lenses take a particularly simple form.Since the distribution method incorporates a pre-focusing function whereeach facet acts in an independent manner, the collector may be a simple,plano-convex lens with flat side towards its receiver array. A slightamount of asphericity may be added to correct for any slight globaldistortions present. Additionally, the collectors are amenable torealization as simple Fresnel lenses produced as a single layer ofmolded plastic only a few millimeters thick.

If the broadcast lenses are also fabricated as (segments of) Fresnellenses, the entire lens array may by molded as a single plastic form afew millimeters in thickness. This feature greatly reduces themanufacturing and assembly costs of the resulting interconnect.

Another benefit of restricting the distribution of light from eachemitter is that the individual beams from each facet are pre-focused tolie within the acceptance aperture of each collecting lens. Bycontrolling the size and shape of images falling on the collecting lens,it is possible to provide a finer detail of control over the emitterimages at the focal plane. For example, one may achieve closeregistration of the focal pattern with the receiver grid, a result thatis simply not possible with a simple distribution system and collectinglenses of one or two surfaces. In addition to improved registration, thespot size is controlled by altering the shape of those beams enteringthe collecting lens aperture at more oblique angles. Typically, obliquebeams produce highly distorted images which provide a poor match to thedesired circular focal regions.

The focal region is defined by a circular disk centered at a givenreceiver having sufficient intensity anywhere within the disk. Thus, thelarger the diameter of the disk, the more the design is able toaccommodate mechanical misalignments, dimensional changes due tooperation over a wider range of temperatures, and a wider range ofmechanical shocks and vibrations. The size of these disks are limited bythe spacing of the receivers and the need for avoiding cross-talkbetween receivers. Control over the focal-region size allows thedesigner to achieve small, intense image regions when eitherlow-sensitivity receivers are used or when the system must be madesmaller than otherwise practical. At the other extreme, large imageregions with good registration become possible if the system is to beused under conditions of severe mechanical vibrations and widetemperature ranges.

Overview and Problem Statement

A particular preferred embodiment includes an 8-way, 4-module systemwith 8 emitters in each module giving 32 emitters in the interconnect.Referring to FIG. 37, the large circles 3810 and labeled from 1 to 32represent both the emitters and associated broadcast lenses. The smallcircles 3820 represent the four sets of 32 emitters. Each receiver islabeled with a number corresponding to its transmitting emitter. Thus,circle 3810 with label 1 represents a broadcast lens that sends light toreceiver 3820 (small circles) with label 1 in each module 3830 labeledModule #1 through Module #4.

Referring to FIG. 38, the electo-optic or EO plane 3910 contains boththe emitters and receivers. The lens plane 3920 is located a distance3930 labeled S from the EO plane 3910. The lens plane 3920 is defined aspassing through the apex of the focusing surfaces of each collectinglens. This plane also contains the broadcast lenses, positioned as thecollecting lenses. The second surface of the collecting lenses (notshown) lies between the lens plane 3920 and the EO plane 3910. Themirror image 3940 of the lens plane is located a distance 3950 labeled Lfrom the EO plane 3910. The mirror 3960 is located halfway between theplane 3920 and the (mirror image) plane 3930 at distance 3970 labeled M.The focal plane 3980 is located at distance 3990 labeled F from the EOplane 3910.

The magnification of the system is controlled by the distances definingthe geometry, specifically the emitter-surface to broadcast-lensdistance 3930 and the distance from the broadcast lens to the mirrorimage of the collecting lens 3950. It is generally desirable to haveboth the broadcast lenses and the collecting lenses lying in the sameplane 3920, with a mirror 3960 lying some distance beyond that plane.The purpose of the mirror 3960 is to fold the optical paths, allowingall lenses to lie in the same plane (the lens plane 3920) and theelectro-optics including emitters, receivers, and associated circuitryto similarly lie in a single plane (the electro-optic or EO plane 3910),usually situated at some distance 3930 from the lens plane. Typicaldistances for a 4-module system with a module face of 100 by 100 mm areS=65 mm from the EO plane to the lens plane, and M=200 mm to the mirror.

Once the system geometry has been chosen, the type of distributionsystem may be selected. Noting the particular inherent divergence of thelight from the emitters is the first step in specifying the distributionoptics. If the emitters include narrow-beam lasers, an additional opticmight be required to spread the light from an emitter so that thebroadcast lens is adequately illuminated when placed at a convenientdistance from the emitter. If the emitted beam is so wide that thebroadcast lens must be placed too close for design purposes to theemitter, an additional optic might be required to narrow the emittedbeam. In a typical system, however, a vertical-cavity, surface-emittinglaser may be chosen for the light source. The 92% power envelope istypically around 23 degrees (full angle of the emitted quasi-Gaussianbeam) and requires no intervening optic when using (approximately) a 26mm diameter broadcast lens some 65 mm from the emitting surface.

First Solution—Simple as Possible

The simplest possible broadcast lens results from choosing a systemgeometry that accommodates the natural spread of the emitters. Simplyallow the emitter light to spread out, reflecting from the mirror andback onto the lens plane, which now includes four collecting lenses and32 holes (if needed) for the 32 naturally diverging beams. The drawbackto this scheme is that the amount of light from a corner emitter, forexample, may not adequately illuminate the collector in the diagonallyopposite module unless the emitter is chosen to be powerful enough.Supposing an adequately powerful laser, collectors closer than thefarthest one receive considerably more light than they need, all themore so if the spreading beams are Gaussian in character. Thisparticular situation is rather unique and restrictive. Moresophisticated distribution systems are desired to allow the designermore freedom of choice over system geometry and the ability to useemitters with minimal power.

Wedges—Next Step in Sophistication

The next simplest broadcast lens directs the light to fall moreuniformly onto the lens plane. For example, if the distances betweensource and broadcast lens are chosen so as to fully illuminate thebroadcast-lens aperture and the distances from the broadcast lenses tothe unfolded or mirror image of the collecting lenses are properlychosen, then the broadcast optic need not possess any focusingproperties, serving the sole function of directing the several beams oflight so that they adequately illuminate the several collecting lenses.The form of such broadcast optics then becomes that of a simple opticalwedge or circular section of a prism, which merely directs the broadcastbeam of light from each emitter so as to adequately illuminate each andevery collecting lens in the system.

Each wedge has only two design parameters, the orientation of the tiltedsurface with respect to the geometric center of the set of collectinglenses, and the angle of the tilted surface. Thus, both the design andfabrication of the wedge broadcast lens is straight forward andinexpensive.

Simple Broadcast Lenses

The next step in sophistication of the distribution system was describedabove under Related Art. Here, a negative curvature is added to thewedges so that the light from each emitter spreads out at a rate fasterthan the inherent beam spread. This allows the mirror to be placedcloser to the EO plane than in the case of the simple wedge, resultingin a more compact system. Alternatively, a broadcast lens with positivecurvature requires that the mirror be placed farther from the EO planethan in the case of the simple wedge. In this way, the interconnectdesigner has some control over the size and aspect ratio of the system.

The problems of distortion of the focal plane with attendant globalspherical aberration and unacceptable coma for those images of emittersfar from the system axis are not addressed by this system unless acomplex collector configuration of multiple-element lenses are used,much as is done in the design of flat-field, wide-angle lenses. Thissolution typically requires a 5-to-7 element collecting lens and becomesprohibitively expensive in a system containing many modules.Additionally, the emitter power required grows proportionally to thenumber of modules. As an example, emitters with an average power of 45mW are needed to adequately service a four-module system based on wedgedistribution. Going from four modules to 16 modules, increases therequired emitter power to 180 mW. As emitter power increases, thedriving electronics becomes more difficult to implement and the powerdissipation of the system increases. Using wedges, over 90% of the lightdoes not reach the collectors as their apertures must be considerablyrestricted to aid in suppressing optical distortions. Should this wastedlight be properly used, the example of the 16-module system wouldrequire approximately 18 mW per emitter instead of 180 mW.

Distributing Facets

The next step in controlling the beams of light from each emitter is todesign a broadcast lens that carefully controls and directs light tofall ideally only on the collector apertures. In this way, littleoptical power is wasted and both distortions of the focal plane anddistortions of individual emitter images may be reduced.

To achieve full control over the distribution of emitter beams in bothextent and shape, the broadcast lens should include multiple facets, onefacet for each collecting lens in the system. This is illustrated inFIG. 39, which shows a four-faceted broadcast lens for the preferredembodiment of four modules. The facets 4010 are sectors of a circle ofequal area and numbered from 1 to 4. The boundaries 4020 between thefacets are shown as lines defining the facet edges. Each facet 4010 hasa central axis 4030 which is oriented at an angle 4040 with respect tothe a rectangular coordinate system centered at the junction of the fourmodules as depicted in FIG. 37.

In the 32-emitter system, there are 32 broadcast lenses each with fourfacets, for a total of 128 facets. Each facet is determined by itsorientation and associated facet lens. Typically, a facet lens is asimple plano-convex optic whose center is placed in a particularlocation with respect to the facet axis and whose diameter must extendto cover the entire facet in question. As such, there are 128 suchlenses to be defined as to curvature, diameter, and location withrespect to the center of their respective broadcast optics. Each facetis a particular segment of one of these lenses; one may think offabricating a lens and then cutting out a small segment in the shape ofa facet 4010 and then assembling four such segments to form the entirebroadcast lens.

Symmetry Considerations

As shown in FIG. 37, the system exhibits considerable symmetry. Eachmodule is rotationally symmetric with the other modules in the system.This fact alone means that only a total of 8 different broadcast lensesare required, this group of 8 being replicated in each module. Broadcastlens 3810 labeled 2 is a mirror image of broadcast lens 3810 labeled 4,but this pair is not rotationally symmetric in that one cannot beobtained by a physical rotation of the other. Proceeding in this fashionthrough the other lenses in the module establishes that the 8 broadcastlenses are each different from the other.

FIG. 40 tabulates, in Table I, the symmetry properties of the 32broadcast lenses in the four-module system. Column 1 of the Table Irefers to the 8 lenses in 3830 of FIG. 37 labeled Module #1. The otherentries refer to the labels for broadcast lenses on other modules. Thesymmetry is indicated by the rows of the table. For example, broadcastlens 3810 labeled 1 is found in row 1 column 1 of Table I. By rotatingthis lens 90 degrees about the origin O of FIG. 37, one obtainsbroadcast lens 3810 labeled 22. An additional rotation by 90 degrees,yields broadcast lens 3810 labeled 32, and a final rotation by 90degrees yields broadcast lens 3810 labeled 11. In this way, each of the8 different lenses is rotated multiple times to obtain the full 32required broadcast lenses. The table captures this rotational symmetry.

Facet Mapping

Before the facet parameters may be determined, it is essential to knowwhich of the 128 different facets directs its light onto which of thefour collecting lenses. First, it is obvious that each of the fourfacets in a particular broadcast lens must direct light onto acollecting lens. The question then becomes, which facet points to whichcollector and does it matter? By assigning collectors to particularfacets in a regular fashion, the symmetry of the system can be preservedand a simplified mapping that aids in lens construction can be found. Anexample of such a mapping for broadcast lens 3810 labeled 8 is shown inFIG. 41 where 4110 indicates the broadcast lens 3810 labeled 8. Facet4120 labeled 1 directs light to collecting lens 4130 labeled 1 alongdirection 4140. This set of mappings can be describe as a set of numbers{8,1,1} meaning facet 1 of broadcast lens 8 directs light to collector1.

A table of such assignments can be constructed for the entire set of 8unique lenses. This table can then be replicated 3 additional times withdifferent rotation angles assigned to each group. The result is a mapfor the entire set of 128 facets connecting to four collecting lenses.Such a table is shown in FIG. 42 which is a tabulation of the symmetryproperties of the 128 facets comprising the 32 broadcast lenses.

Referring to FIG. 42, column 1 of Table II indexes the 8 differentbroadcast lenses required in the preferred embodiment. The headings ofcolumns 2, 3, 4, and 5 in Table II indicate the module number (M1through M4) referring to modules 3810 of FIG. 37. The heading numbers inparentheses refer to the angle, in degrees, of rotation required toorient the broadcast lenses 1 through 8 of column 1 to the particularmodule so indicated. For example, the broadcast lenses 1 through 8 ofcolumn 1 are rotated by 0 degrees for assignment to module 3810 labeledModule #1 of FIG. 37. This is indicated by the heading M1(0) in TableII. The entries in columns 2, 3, 4, and 5 refer to the mapping of thefacet numbers, indicated by the four positions in the 4-tuples ofnumbers, to the collecting lens indicated by the contents of thatposition. For example, broadcast lens 4110 labeled 8 in FIG. 41 andindicated by entry 8 in column 1 of Table II has assignment of facet4120 labeled 1 in FIG. 41 to collecting lens 4130 labeled 1 in FIG. 41,as indicated by the number 1 being in the first position of thecorresponding 4-tuple. Referring to FIG. 41, the assignment 4140 isrepresented by the contents of position 1 in the 4-tuple of column 2 ofTable II of FIG. 42, corresponding to the entry 8 of column 1. As afurther example, lens 8 of column 1 is rotated 90 degrees to map intomodule 2 as shown by the heading M2(90) of column 3. Referring to entry8 of column 2 in Table I of FIG. 40, we find the number of thecorresponding broadcast lens to be 19. The 4-tuple in row 8 of column 3of Table II contains the assignment {5,1,2,4} which indicates that facet1 of broadcast lens 19 is to direct its light to collector 3 of Module3, and so on.

Additional Facet Symmetry

Table II shown in FIG. 42 exhibits a great deal of additional symmetryin that all facets in a given module are similarly oriented. Theseadditional symmetries reduce the number of unique facets from 32 to 18,which may also be verified by constructing figures similar to FIG. 41for all 32 broadcast lenses in the system.

Defining the Facet Lenses

FIG. 38 refers to a set of four numbers, {F, L, M, S}, that specify thegeometry of the system. In addition, the module size or spacing isrequired to fix the size of the object, which is the emitter grid. Thismodule size 3850 is referred to as P in FIG. 37. Since the mirrordistance, M, is given by half the sum of L and S, it may be consideredto be a derived parameter. The specifying set of numbers is then {P, S,L, F} and determines both the magnification (if a single-surfacecollector is used) and the overall size of the optical system. With aparticular assignment to this set, values for any of the facet-lensparameters may be computed.

Consider 4010 of FIG. 39, which, in the preferred embodiment, is onefourth of a circle (in the general case, the aperture of the broadcastlens need not be circular and the number of sectors is equal to or oneless than the number of modules in the system). This one-quarter circle,with facet boundaries 4020, is a section of a lens with a certainspecified location, diameter, radius of curvature, R, and shapeparameter k. The curvature and shape parameter are related to the heightof the lens surface by the standard surface equation of an axiallysymmetric lens, given by

$\begin{matrix}{{Z(r)} = \frac{r^{2}}{R\left( {1 + \sqrt{1 - \frac{r^{2}\left( {1 + k} \right)}{R^{2}}}} \right)}} & (4)\end{matrix}$where Z is the height of the surface at radius r and k is a shapeparameter. For k=0, the equation becomes that of a spherical surfacewith radius of curvature R. For k=−1, the surface is a paraboloid ofrevolution. Any facet lens, from which the corresponding facet sector istaken, requires a location and diameter in addition to the parameters Rand k of Equation (4). To complete the specification, all facet lensesare taken as plano-convex with refractive index n.

To establish the center of a facet lens, refer to FIG. 43, whichillustrates a broadcast lens 4310 and a particular facet 4320 of thebroadcast lens delineated by the facet boundaries 4330. A facet axis4340 bisects the facet and defines a direction for locating the centerof the facet lens. The distance 4350 labeled c is the first centerparameter and is measured from the center of the broadcast lens 4310along the facet axis 4340. A direction, from the point along the axisspecified by c to the center of the collecting lens, which is locatedabove a module of FIG. 37 is established. The second center parameter isa distance 4360 labeled d along this direction. The center of the facetlens 4370 is located at this point.

The radius 4380 of the facet lens labeled h is specified so that thelens completely covers the facet 4320. An outline 4390 of the resultingfacet lens is shown in the figure.

A facet lens is then defined by the parameter set {c, d, h, R, k}. Oncethis set has been determined for the 18 different facet types, theentire 128 facets may be manufactured and assembled into the set of 32broadcast lenses. An alternate approach is to manufacture four sets ofthe 8 different broadcast lenses, wherein each lens is molded from aspecially designed, four-segment mold. Four sets of these 8 differentlenses are required to complete the broadcast optics of the four-moduleinterconnect.

Computing the Facet Parameters

As shown in the section on Collecting Lenses, a collecting lens isgenerally not centered over a module face. The collecting-lens centersmust be known to be able to specify the parameter d in the facetparameter set {c, d, h, R, k}. Assume that the collecting lens centersare known, then the facet parameter set {c, d, h, R, k} is determined bya solution to an optimization problem that involves tracing a set ofrays from the source or emitter lying a distance (3930 of FIG. 38labeled S) below the broadcast lens in question. Only rays incident onthe desired facet are required.

Optimizing the parameter set requires choosing initial values for all 5parameters and tracing the set of rays from the source, through thefacet lens. The resulting pattern of rays is examined on the lens plane3940 as to location, extent, and shape. A quality factor is computedbased on these measures, and the process is repeated with a differentset of parameters. An efficient way of choosing parameter sets toexamine is provided by the simplex method of multidimensionaloptimization.

Once an initial set of parameters has been found, a refined set may bederived by allowing the set of rays to refract through the collectinglens and fall on focal plane 3980. Once again, the pattern of rays isexamined as to location, extent, and shape. A quality measure at thisstage depends upon the desired size of the focal pattern, which iscontrolled by the parameter R; the position of the focal pattern, whichis controlled by the two location parameters, c and d, as well as by R;and the shape, which depends on parameter k. In reality, all 5parameters interact to affect the quality measures. Again, the simplexmethod of optimization is the most efficient one found for such a set ofinteracting parameters.

The results of such an optimization is summarized in FIG. 44, Table III,which was computed by considering all 32 facets that point to Module #1.This calculation demonstrated that only 18 of the facets were unique.

Each of the 18 facet sets displayed in Table III belong to more than onephysical facet. For example, from the symmetry diagrams and Table I,facet #1 is found in broadcast lenses 1, 11, 22, and 32 where it isrotated in position by 0, −90, +90, and 180 degrees, respectively. Asanother example, consider facet#3 of Table III. This facet is found inModule#1 lens 3 and lens 6. Lens 3 is also lens 17, 30, and 16 byrotation and lens 6 is also lens 24, 27, and 9 by rotation. Thus,facet#3 is found in the 8 lenses {3, 17, 30, 16, 6, 24, 27, 9}.

Location of the 18 Facets

A map assigning the 18 facets to broadcasts lenses and to particularlocations in these lenses is displayed in FIG. 45, Table IV. This tabledisplays a tabulation of the location of the 18 unique facets foundwithin the 32 broadcast lenses. The first column refers to the broadcastlens index 3810 in FIG. 37. Columns 2, 3, 4 and 5 contain the numbers 1to 18, which refer to the facet-parameter sets of FIG. 44, Table III.For example, the first facet of broadcast lens #3 has parameter set 3,or the third row in Table III. This is facet 4010 labeled 1 in FIG. 39.Likewise, the second facet 4010 labeled 2 has parameter set 16 found bycontents of row 16 in Table III. This procedure indicated here allowsone to map any set of facet parameters to its appropriate broadcast lensand facet location.

Note that any particular facet index (1 to 18) is found multiple timesin Table IV. As an example, facet index 18 is found four times in thebody of the table, namely in broadcast lens 1, 8, 25 and 32. These arelenses along the main diagonal of FIG. 37 and share only rotationalsymmetry with each other. By contrast, facet index 17 is found eighttimes in the table and belongs to broadcast lenses 2 and 4, which aresymmetric by reflection across the main diagonal, as well as thereflection-symmetric pairs 10 and 20, 13 and 23, and, finally, 29 and31. These pairs are rotationally symmetric to each other (10 rotated to23 and 20 rotates to 13, and so on).

Local Distortions Reduced by Anamorphic Facet Lenses

The 8 images of the emitters in a particular module are axiallysymmetric with respect to that module, thus emitters 3810 labeled 1through 8 are symmetrically located with respect the module 3830 labeledModule#1 center. As such, they experience very little distortion.However, beams from emitters located in other modules in the systemstrike the collector in question at increasingly oblique angles as thedistance to the particular emitter is increased from the specifiedcollector. These oblique beams produce highly distorted images on thefocal plane. The position of these images is controlled by the power andplacement of the lens segment comprising the particular facetresponsible for the image. However, the aspect of the distorted imagesbecomes large for distant facets. This distortion reduces the opticalpower falling on the target receiver and reduces the effective diameterof the focal region, leading to increased susceptibility to both staticand dynamic misalignments of the components. Additionally, an image thatis highly distorted may partially illuminate a neighboring receiver,increasing the possibility of cross talk in the system.

By designing facet lenses to be anamorphic in character, the distortedimages can be made more circular, thus providing a more uniformillumination of the receiver region. A simple anamorphic lens has anelliptical surface instead of the usual spherical surface. Theorientation of the ellipse (direction or alignment of the major axis) ischosen to lie along the line between the center of the facet lens andthe center of the targeted collecting lens. By varying the eccentricityof the elliptical surface, the aspect ratio of the image spot may becontrolled.

Collecting Lenses

Collecting Lens for an 8-Way, 2×2 Configuration

Each collecting lens is approximately centered over its correspondingmodule; more precisely, the axis of the collecting lens passes close tothe center of its module, which is also the center of the receiverpattern. Referring to FIG. 37, the system axis is a vector {0,0,1},normal to the center 3840 labeled O while the center of Module #1 islocated at {−P/2,−P/2} where P is the dimension of the side of a modulecenters indicated by 3850 in FIG. 37, and hence the spacing betweenmodule centers.

The emitter grid, as depicted in FIG. 37, is a square lattice withpoints centered at {0,0} with lattice points spaced by P/3 in eachdirection, starting with the lower left emitter 3810 labeled 1 locatedat {−5P/6,−5P/6}. Emitters corresponding to lattice points at {±P/2,±P/2} are omitted as these points specify the centers of the receivergrids.

A ray emanating from a hypothetical emitter located at {0,0,0} andhitting the collecting lens at its center {a, a, L} for some value a,will refract at the collecting lens but not change direction on passingthrough the lens. This is so since the ray intersects the surfaceprecisely at the lens axis where the normal is directed along the systemaxis direction {0,0,1}. The ray will, however, be deflected by an amountdepending on the thickness of the plano-convex collecting lens and theindex of refraction. In the thin-lens approximation, this thickness willbe ignored.

This hypothetical ray is required to strike the center of the receiverpattern (module center) at the focal plane. That is, the ray must passthrough the point {−P/2,−P/2, F} for a 2×2 configuration of modulescentered on a square grid with pitch P.

Referring to FIG. 38, S is the distance 3930 from the plane of emitters3910 to the lens plane 3920, L is the distance 3950 from the plane ofemitters 3910 to the mirror image of the lens plane 3940. The distance3990 to the focal plane 3980, F, is then given by (assuming thatemitting and receiving surfaces lie in the same plane)F=L+S  (5)and the distance 3970 to the mirror 3960 is given byM=(S+L)/2  (6)where both distances are referenced to the emitter plane.

Faceted Broadcast Lenses Allow Simple Collecting Lenses

A ray from each emitter to the lens array directed along the system axis{0,0,1} is refracted by the broadcast lenses (located in the lens planeabove each emitter). These central rays each reach the surface of thecollecting lens on the its axis. Intersection of collection of these 32rays with the second (exit) surface of the broadcast lenses defines thevirtual emitter grid. That is, the virtual emitter grid is located atdistance S from the actual emitter plane. Referring to FIG. 46, theposition and extent of this grid, along a diagonal between the two mostdistance emitters, for example, emitter 3810 labeled 1 and emitter 3810labeled 32, is termed object 4608. The mirror, 4610 is shown forcomparison to FIG. 38.

The mechanical reference plane supports both receivers and emitters,while the optical reference located at z=0 is the plane 4606 containingthe emitting surfaces. The lens plane 4612 defines the z-position of thefront surfaces of the set of lenses in the system. The location of theback surface of the lenses is referenced from this plane and determinedby lens thickness (not shown).

The first step in designing the facet lenses is to compute the locationof the collecting lens from the geometry specified by the set of numbers{P, S, L, F}. This location must then be corrected by the offsetexperienced by the central ray as it is refracted by the collectinglens. In the thin-lens approximation, the correction vanishes.

The simplest collecting lens includes a curved or focusing surfacedfollowed by a planar surface parallel to the reference plane. The lensaxis is taken to be the vector {0,0,1}, or normal to the referenceplane. The geometry illustrated in FIG. 46 defines the magnification ofthe lens and hence the size of the receiver array. That is, the size ofreceiver grid or image 4609 (receiver spacing and array size) isdetermined by the set {P, S, L, F} and the choice of a plano-convexcollecting lens (a collecting lens with multiple surfaces will produce areceiver grid of a different extent). The center of the collecting lensin the lens plane is likewise determined by this set of numbers whencorrected for the lens thickness and the refractive index of the lensmaterial. Again, in the thin-lens approximation, this correctionvanishes.

Geometric Magnification & Collecting Lens Location

The magnification of the collecting lens is defined as the ratio of theimage size to the object size. Since the object is fixed by the geometryof the emitter configuration, the magnification depends on the definingset {P, S, L, F} while holding P fixed. In the ideal case of a thincollecting lens, or equivalently, if the collecting lens is approximatedby a pinhole, the magnification is a simple geometrical ratio involvingF, L, and S. The “module” in the following discussion refers to module3830 of FIG. 37 labeled Module #1.

Referring to FIG. 46, consider the ray 4614 from emitter at 4601 labeledE, located on the emitter plane 4606. This ray is directed along thenormal {0,0,1} until refracted at the lens plane 4611 by the broadcastlens centered at 4604 labeled A. From there, the ray 4614 intersects thecenter of the collecting lens located at 4607 labeled X. The ray 4614then proceeds in the same direction, since the collecting-lens normal isalso directed along {0,0,1} at point X, until it intersects the focalplane 4616 at the lower extent of image 4609 at the point 4620 labeleda. In a similar manner, ray 4615 originating at corner emitter 4602,also labeled E, is refracted by the broadcast lens centered at 3840 andlabeled B. The ray is thereby directed to intersect the collecting-lenssurface at the same point X. Ultimately, this ray intersects the focalplane 4616 at the upper extent of image 4609 at the point 4621 labeledb. The size of the image 4609 is found by the similarity of the twotriangles ABX and abX. The point 4619 labeled f is located at the centerof the module and, hence, the center of the receiver pattern. Extend aline from f, parallel to the direction {0,0,1} and back to the lensplane 4611. This line intersects the lens plane 4611 at point 4617labeled e and also intersects the mirror image of the lens plane 4612 atpoint 4618 labeled C. The segment eC is then the height of triangle ABXwhile the segment Cf is the height of triangle abX. By similarity of thetwo triangles, it is evident that geometric magnification G given byEquation (7), as

$\begin{matrix}{G = {\frac{ab}{AB} = {\frac{Cf}{eC} = {\frac{F - L}{L - S} = {\frac{S}{L - S} = \frac{S}{2\left( {M - S} \right)}}}}}} & (7)\end{matrix}$where segment ab is the height of the image 4609 and segment AB is theheight of the object 4608 and the last two ratios are found fromEquation (5) and Equation (6), respectively.

To find the location of the center of the collecting lens, or thepinhole in the pinhole-lens analogy, consider the point 4605 labeled Owhich lies at point {0, 0, S}. A ray 4613 from (virtual) emitter 4603labeled E to the point O is then directed to the point 4607 labeled X,the center of the collecting lens. An extension of this ray intersectsthe focal plane 4616 at the point 4619 labeled f, which, by design, isthe center of the module and receiver pattern. The two triangles Oef andXCf are similar. The offset of the lens center from the module center isthe segment CX and found from the similarity ratio given by Equation (8)as

$\begin{matrix}{\frac{CX}{Oe} = {\frac{Cf}{ef} = \frac{F - L}{F - S}}} & (8)\end{matrix}$Segment Oe is simply half the module-face width, so the offset, D, isgiven by Equation (9), as

$\begin{matrix}{D = {{CX} = {{\frac{P}{2}\frac{F - L}{F - S}} = {{\frac{P}{2}\frac{S}{L}} = {\frac{P}{2}\frac{S}{{2M} - S}}}}}} & (9)\end{matrix}$where the Equations (5) and (6) are used to obtain the last two ratios.

The two procedures outlined above determine both the geometricmagnification of the system and the location of the collecting lensesgiven the parameter set {P, S, L, F}, and are correct in the thin-lensapproximation. A minor correction can easily be made for the case of afinite-thickness lens; such a correction usually involves tracing rays4614 and 4615 through the chosen lens of desired thickness and takingthe normal to the lens at point intersected by the rays to be directedalong {0,0,1}.

Corrections for a Thick Collecting Lens

As noted above, the values of the geometric magnification, G, and theoffset, D, are both exact in the thin-lens approximation. This is sosince refraction of a ray incident on the axis of a thin lens does notshift in position when traversing the lens. In a more practicalsituation, where the lens has finite thickness, refraction at the secondsurface, even if planar, will shift the ray's position according toSnell's law. Referring to FIG. 47, the first surface 4708 of the lensrefracts rays 4701 and 4702, which are incident on the surface axis orcenter 4707. Passing to the second or back surface of the lens 4709,these two rays are refracted into rays 4705 and 4706. Unrefractedversion of these two rays are shown as dashed lines, 4703 and 4704. Theunrefracted rays lie outside of the surface formed by the refractedrays.

From this figure, based on Snell's law of refraction, it is evident thatthe magnification of the system is reduced by an amount related to thelens thickness and the angles of incidence of the extreme rays above andbelow the lens center. (A ray at a steeper angle undergoes moredeflection, while one along the lens axis undergoes no deflection).Tracing these rays in a situation of finite thickness, produces theactual system magnification, which is typically a few percent lower thanthe geometric magnification.

A central ray such as ray 4613 shown in FIG. 46, will still be incidenton the center of the collecting lens. However, since the collecting lensis not on the system axis {0,0,1}, this central ray will undergo aslight deflection, which may be calculated in the same manner asmentioned above. To ensure that this central ray strikes the center ofthe module and hence receiver pattern, this deflection must besubtracted from the offset D determined in Equation (9).

Summary of Design Based on Geometric Magnification

The design of a four-module system is straightforward when the geometricmagnification, G of Equation (7) is used. Assume that the correctionsfor lenses of finite thickness, as discussed above, have been made. Thefacets are then computed as described above, and the R and k of Equation(4) for the collecting lenses are chosen to optimize the size and shapeof the set of focal patterns at the focal plane. This is in contrast tothe choice of parameter set {c, d, h, R, k} chosen to optimizeindividual focal spots belonging to each facet after an R and k for thecollecting lens have been selected.

The actual magnification increases with S and decreases with L, allowingthe designer to vary the image size. A determining factor for S is thespread of the emitted beam and the diameter of the broadcast optic. Abeam emitted into a narrow cone will require the broadcast lens to liefar from the emitting surface which implies a large image size.

An interconnect designed in this way will be optimal for the (corrected)geometric magnification based on the set {P, S, L, F} withsingle-surface collecting and facet lenses conforming to Equation (4).The simplicity of the resulting optics is attractive for manysituations. However, the system magnification is fixed for a givenmirror distance within a small variation in lens-plane distance for agiven module-face size. If this restriction of the magnification is tooconfining, a second collecting surface must be added.

Split or Compound Collecting Lens

Certain situations in the design of an interconnect might arise wherethe defining set {P, S, L, F} is specified, but a receiver griddifferent in size, location, or aspect ratio is desirable. Thesevariations in receiver grid geometry may be effected by a secondcollecting-lens surface. For example, if it is necessary to shrink thereceiver grid while keeping it centered in the module face whilemaintaining the aspect ratio of the emitter grid, then a secondcollecting surface with converging properties must be added between thefirst surface and the focal plane. Conversely, a second surface withnegative curvature will expand the image size, increasing the effectivemagnification above the geometric magnification.

More specifically, since it is desirable (but not necessary) to placeboth broadcast lenses and collecting lenses in the same plane, the focallength of the collector depends on distance S as well as the acceptanceaperture of the broadcast lens. It is generally desirable to fill thisaperture out to the 85-to-95% spread of the emitters so as to makeefficient use of the light sources. With a smaller beam divergence, thebroadcast lens must be placed farther from the emitter, implying alarger distance S and a larger magnification. The resulting image mightbe so large that the receiver grid interferes with the emitter grid.This situation requires a second collecting surface with convergingproperties to reduce the image size. Conversely, should the emitter havea large beam divergence, the broadcast lens must be situated closer tothe emitter, resulting in a smaller magnification and receiver grid. Inthis case, the solution is to provide a second collecting surface withdiverging properties to enlarge the image size.

Options for the second collecting surface are twofold. The first optionis to replace the second planar surface of the collecting lens with acurved surface, allowing adequate separation between the two surfaces.An increased thickness would ensure that each central ray from eachemitter is refracted to a different location than it would have beenwith no or minimal separation of the two surfaces; such a separationeffectively alters the magnification. Additionally, local surfacevariations will play less of a role in distorting the receiver grid on athicker lens as the image of the emitter grid at the second surface willbe larger and more spread out, hence less susceptible to local surfacevariations.

The second option is to employ a distinct lens spaced a certain distancebetween the first lens and the focal plane. This spacing becomes animportant design parameter and also allows both collecting lenses to berealized as Fresnel lenses.

The axis of the second surface will not coincide with the axis of thefirst surface. The reason for this is that the hypothetical central rayemanating from the center of the virtual emitter grid intersects thecollecting lens at an oblique angle. That is, neither the object (thearray of emitters) nor the image (the array of receivers) lies on thelens axis.

If the collecting lens includes a single optic with two curved surfaces,the lens must be “split” parallel to the reference plane so that the twosurface axes are offset by a certain amount. This offset is determinedby simple geometrical considerations and depends on the thickness of thelens as well as the defining parameter set. If two lenses are used, asmight be the case if thin Fresnel lenses are chosen for the optics, theoffset between the two axes depends on both thicknesses, the refractiveindex, and the distance between the two lenses.

Referring to FIG. 48, the ray 4805 from a corner emitter and the ray4806 from a diagonally opposite corner emitter both intersect the firstsurface at the lens plane 4801 at the center of the first surface 4811.If the second surface 4802 has positive curvature (is a converginglens), the refracted rays 4808 and 4810 will bend inwards, as shown.These two refracted rays define the extent of the image 4803. If thesecond surface 4802 had no refractive effect, the two incident rayswould be the unrefracted rays, 4807 and 4809, delineating larger imageaccording the geometric magnification of the system. Thus, a convexsurface placed between the first surface and the image plane reduces theimage size. Conversely for a concave surface (negative curvature).

The central ray 4804 must still intersect the center of the receiverpattern and, hence, remain unaffected in direction by the secondsurface. This can only happen in the situation depicted if this rayintersects the axis of the second surface 4812. This illustrates thatthe axis of the second surface cannot be coincident with the axis of thefirst surface. The second-surface axis must lie farther from the systemorigin than the axis of the first surface. The geometry of thissituation is evident from the figure, which may be used to compute theprecise position of the second surface with respect to the first, giventhe distance 4813 labeled t between the two surfaces. The angle centralray 4804 makes with the system axis {0,0,1} is the inverse tangent ofthe ratio of the distance Oe to the distance ef of FIG. 46. The distancebetween the two axes, which pass through 4811 and 4812 respectively, isthe tangent of this angle times the distance between the two centers4811 and 4812 measured along the system axis {0,0,1}. Thus, the axialdistance 4814 labeled q is given by Equation (10), as

$\begin{matrix}{q = {{t\frac{Oe}{ef}} = {{t\frac{S}{F - S}} = {{t\frac{S}{L}} = {t\frac{S}{{2M} - S}}}}}} & (10)\end{matrix}$

Of course, in a system with a central module, such as 9 modulesconfigured in a square array, the collecting lens above the centermodule has both object and image on axis. In this case, the there willbe no offset between the two axes and the axis of the collecting lenscoincides with the axis of the module and the axis of the emitter grid.That is, the collecting lens, both first and second surfaces, for thiscenter module is located precisely at {L, 0, 0} and {L+t,0,0},respectively.

Extending the methods to other module configurations

The system with 4 modules arranged in a square is the simplest,non-trivial configuration. All collectors in this configuration areidentical and the optics may be realized with a simple, single-surfacecollecting lens if the geometric magnification is sufficient to definethe required receiver grid.

Other configurations, serving different applications are possible.Consider four modules arrange in a row. The form factor of this 1-by-4four arrangement has obvious advantages over the more compact, 2-by-2arrangement described as the particular preferred embodiments. Forexample, forced-air cooling of the 1-by-4 arrangement may well be aneasier task than forcing air through two layer of electronics.

Numbering the modules in the linear array with the numbers 1, 2, 3, and4, symmetry considerations show that there are two different collectors(location and curvature) replicated twice, once for the left half(numbers 1 and 2 say), and the other for the right half. There are also,in an 8-way module, 8 different broadcast lenses required in each moduleon the left half, which are replicated, by rotational symmetry, for theright half. That is, lenses for module 1 are identical to those formodule 4, and those of module 2 are identical to those of module 3.

The situation is a bit more complicated with nine modules arranged in a3-by-3 fashion. In this case, by symmetry considerations, there are atotal of three different collecting lenses and nine different broadcastlenses. For a 4-by-4 arrangement, there are three different collectinglenses, with the proviso that the placement of these collectors followsa reflection about the several symmetry axes. The number of distinctbroadcast lenses jumps to 32 with 54 distinct facets among the total of8×16×16 or 2048 in all.

If all collectors are to be placed in the same plane, then FIG. 48implies that two of the collectors in the 1-by-4 case will requireeither split or compound lenses; while a minimum of 5 in the 3-by-3example will need to be split or compound. For the 4-by-4, either 8 or12 of the lenses will be split or compound. Of course, for anymagnification other that the one determined by geometry (as given byEquation (7)), all lenses will be either split or compound.

Macro Distortions Reduced by Correcting Collector from Spherical toAspheric

A distortion of the image or focal plane may still be found in thedistribution-collection methods disclosed herein. By adding smallaspheric expansion terms to the standard spherical terms in theexpression for the surface of the collecting lens, it is possible toreduce the effect of such focal-plane distortions.

Summary of Method & Benefits

The invention includes two inter-related parts: (1) designing a facetedbroadcast lens in conjunction with (2) an appropriate collecting lens.This combination solves many of the optical and intensity problemsinherent in a broadcast FSOI. Among these problems are focal planedistortion, image-region distortion at individual receivers, inadequateintensity, especially when scaling to larger systems.

The above discussion has presented design methods for realizing thesimplest possible optical system involving an array of coplanarbroadcast and collecting lenses. In this simplest case, it is feasibleto realize the lens array as a molded array of Fresnel lenses in asingle sheet of nominal thickness. Both broadcast (facet) lenses andcollecting lenses may be plano-convex, resulting in an inexpensiveoptical system.

A minor complication was required to vary the system magnification fromthe geometrical magnification. This change required that a second,curved surface be added to the collector by either making the lensthicker or adding a second lens plane containing this second surface asan additional plano-convex lens, which may also be fabricated as a sheetof Fresnel optics.

ADVANTAGES OF THE INVENTION

The invention provides advantages in the context of supercomputing.Communications between processing nodes is one of the central bottlenecks found in supercomputers. The methods disclosed herein overcome thelatency problems associated with interprocessor communications byinterconnecting all nodes in a system with light. The resultinginterconnect is smaller and faster than existing cross-bar and fat-treemethods. In addition, the invention allows efficient broadcast models tobe directly implemented rather than simulated as is presently done.

The invention provides advantages in the context of switching androuting. Configured as an optical switch, any node in the system canbroadcast information to all other nodes. If each information packet hasan associated routing header, any one or several receiving nodes thatrecognize that header can accept the information packet and transmit itout of the optical switch to the appropriate recipient.

The invention provides advantages in the context of associative memory.In simplest terms, memory association is a method of posing a query asto the presence or absence of a certain item. A code for the item inquestion is broadcast to all portions of the system. These portions aresearched in parallel and any positive responses are reported back to thequerying node. The effect is that of an associative memory. Such anassociative memory can be very large and distributed by making use ofhashing tables at each processing node (module), such hashing tablescontain references to remote memory stores such as disk drives orinternet resources.

The invention provides advantages in the context of sorting and merging.The broadcast capability allows a multiprocessor system to carry outsorting algorithms more efficiently than presently used interconnectmethods. A table or list to be sorted is broken into n small pieces andeach piece is sent to one of n processing nodes (modules) where it is isfinished to coordinate the merging phase. Each processing node (module)then sends its table element-by-element in ordered fashion to themerging node where the results are placed in the final table in sortedorder. Comparisons are done in the merging node (module) to achieve theoverall order based on range information received from each of thepartial-sorting nodes (modules).

The invention provides advantages in the context of communicationsprocessing where one light path is used to simply transmit acommunication stream while the other n²−2 paths split up the data streaminto multiple processes on independent processors, each of which mightsearch for a different pattern or condition without affecting orinterfering with the primary communications path. The invention providesadvantages in communications processing where forward error correctioncan be effectively and efficiently done on the communications stream inplace and on-the-fly. The invention provides advantages incommunications processing where individual data packets representingvoice messages can be decoded into sampled audio, such sampled audio isthen subjected to further processing such as speaker or speechrecognition even as the uninterrupted path through the system continuesto carry the original message.

The invention provides advantages in the context of image processingwhere each portion of the image is sent to a different processor for aparticular type of filtering operation, all such filtering operationstaking place in parallel. The final image is then reassembled at asingle node in the system.

The invention provides advantages in the context of pattern recognitionon signals or images where the probabilities of certain pattern typesare desired. Each of n processors can examine a signal or image inparallel where each examination is essentially testing an hypothesisconcerning a particular pattern. The result of each individual processis a probability of a particular pattern being present. Combining theresults in the Bayesian manner yields the most probable pattern alongwith its absolute probability within the population of patterns beingsearched.

The invention provides advantages in the context of database searchingwhere each processor has access to a different database or a differentpart of a particular database. A machine with n nodes opticallyconnected as in the broadcast method allows such a search to proceed inparallel, effectively speeding up a database search by the number ofprocessors available.

The invention provides advantages in the context of pattern recognition,where data from a subset of sensors, such as a random grouping of pixelinformation from an imaging device, is sent by broadcast to specificpartial-image processors. The entire set of image-processing nodes(modules) can then identify particular pieces of the pattern inparallel. Individual pattern elements are then recognized as belongingto certain patterns. The results are assembled in a coordinating elementand the most probable pattern is identified with the presented image.The paper by W. W. Bledsoe and I. Browning, “Pattern Recognition andReading by Machine” in the 1959 proceedings of the Eastern JointComputer Conference presents a particular example of pattern recognitionthat would benefit by the broadcast method disclosed herein.

More generally, in the usual interconnection methods, typically eitheroptical or electrical (crossbar, electrical multiplexing with fan-out,etc), broadcast is achieved by increased complexity or simply notattempted other than by relaying messages between processors or seriallybetween levels of the interconnect hardware. Optical fan-out is bothinexpensive and simple to accomplish. Electrical fan-out, on the otherhand, is slow, expensive, and difficult to accomplish, introducinglatencies and delays in the message paths. The optical broadcast methoduses optical fan-out, allowing light energy to reach all parts of thesystem from each optical emitter. An added feature of using light forbroadcast is that light from various emitters does not interfere in thefree-space region where the fan-out is taking place. That is, multiplelight channels can occupy the same physical space.

The broadcast model of optical communication within a backplane allowsefficient multiple-instruction, multiple-data (MIMD) operation as wellas the usual single-instruction, multiple-data (SIMD) operation.Broadcast allows parallel database searching. This can be achieved bybroadcasting a query to a distributed database where each portion of thedatabase is interfaced to a processing node (module) of the system.

The broadcast model of optical communication within a backplane allowsasynchronous operations and data-flow architectures. Synchronization canbe efficiently achieved and maintained by broadcasting short messagesconcerning global system status and reporting local processor or clusterstatus. Data-flow computations can be easily coordinated by such shortbroadcast messages.

The broadcast model of optical communication within a backplane allowsboth large-grained and fined-grained problems to run simultaneously. Inthis case, destination codes can be assigned to groups of nodes and suchnodes are not constrained to be near neighbors. Dynamic “local” groupsare may be formed where “local” has a purely logical connotation and notconstrained by physical nearness.

The broadcast model of optical communication within a backplane allowshigh-throughput transaction processing. For instance, by allowing eachprocessing node (module) in a large lightcube array to communicate withseveral transaction stations, a lightcube can handle a large number ofdistributed and local transactions. Coordination between thetransactions and a central data repository can be accomplished bybroadcasting necessary information to coordinating processors as thetransactions occur.

The broadcast model of optical communication within a backplane allowsefficient semaphore use and management. Semaphores can be used tocontrol computing resources by preempting them for in certain situationsand allowing access in others. Semaphore management can become efficientand practical in a broadcast model.

The broadcast model of optical communication within a backplane allowsmultiple hypothesis testing on a single system (e.g., Bayesian parallelprocessing). Bayesian hypothesis concatenation and the particularapplication of Bayesian signal processing are the most consistenttechniques for dealing with data of all kinds. Although preferred bymany, these computationally intensive activities are often approximatedby faster but less accurate methods. A parallel-processing system thatallows broadcast of data to multiple hypothesis-testing nodes will allowthe more accurate Bayesian methods to find wider application.

The broadcast model of optical communication within a backplane enablesdistributed memory access. A significant advantage of a low-latency,message-broadcast model is improved memory access in a distributedmemory system. For example, in a cache-coherent, uniform memory model,the addition of a new node would not be a problem as the new node wouldsimply announce its presence and any reference to the new node would besimply a reference at large, broadcast to all.

The invention is scalable and cost effective. The invention isinherently tolerant to misalignment with no feed-back recovery systemnecessary. The invention facilitates efficient optical communicationand/or computing within and between core switches, terabit routers andcross-connect equipment, especially in central office environments.

PRACTICAL APPLICATIONS OF THE INVENTION

There are many practical uses for the communications power provided bythe invention that have substantial value within the technological arts.A central result achieved by the invention is that of intrinsicinformation broadcast to the entire set of processing nodes (modules).As a computing or data-processing technique, broadcast allows multiplereceiving nodes, simultaneously and without necessity of intervening anddelaying relaying steps, to receive coordinating information as well asallowing data to be processed in parallel. Practical uses of broadcastinclude synchronizing computing activities, efficient communication ofsystem control information, efficient management of semaphores (e.g.,for simultaneous updating of local cache memory from a global memorystore), implementation of a flat-memory model where a system-widedistributed memory is uniformly available to all processing nodes(modules) within a system, asynchronous routing of packet information tomultiple receivers, distributing video information to multiplereceivers, database transaction processing where a single query ispassed to multiple databases and/or distributed to portions of a largedatabase, and pattern matching wherein a pattern is broadcast tomultiple processors each of which examine in parallel a small portion ofthe image and the matching information is broadcast from eachpartial-pattern processor to a central information processor. Inaddition to processing of information, broadcast can be used toefficiently and effectively control information being sent to a varietyof receiving stations, whether local within the system or remote fromthe interconnect and accessed by Ethernet, internet, or other networksand communication channels.

There are many practical uses for the magnitude of computing powerprovided by the invention that have substantial value within thetechnological arts. The invention is useful for simulation and modelingof physical processes. The invention is useful for switching and routingof information. The invention is useful for the management of massivedatabases. The invention is useful for pattern matching andcorrelations. The invention is useful for data analysis and reduction.The invention is useful for image processing and rendering.

A partial list of practical applications for the invention include:nuclear stockpile verification; massive database searches &correlations; drug design; biological simulation and modeling; weathersimulation and modeling; physics & astronomy simulation and modeling;chemistry by design; mechanical engineering structural modeling anddesign (e.g., buildings, vehicle crash testing, etc.); earth sciencessimulation and modeling; biometrics on a massive scale (e.g., voice,face, vital signs, bio patterns, etc.) voice identification and speechtranscription on an accurate and massive scale; economic andsociopolitical simulation and modeling; automatic database creation,management, consolidation and mining; and onboard space-craft andsatellite data processing. Some applications for the invention inswitching, routing, and rendering are: automatic communications anddata-routing center, for instance, gathering, sorting, classifying,correlating, and disseminating all communications; informationmanagement and switching (e.g., a continental-scale data router or other(potentially inexpensive and redundant) continental-sized distributedsystems); pinpoint video for a mass audience (e.g., education,entertainment, and so forth); repository, storage, and deliverysystem(s); real-time film production (e.g., animation, rendering,digital imaging, etc); and a multi-player, video game server. There arevirtually innumerable uses for the invention, all of which need not bedetailed here.

The terms a or an, as used herein, are defined as one or more than one.The term plurality, as used herein, is defined as two or more than two.The term another, as used herein, is defined as at least a second ormore. The terms comprising (comprises), including (includes) and/orhaving (has), as used herein, are defined as open language (i.e.,requiring what is thereafter recited, but open for the inclusion ofunspecified procedure(s), structure(s) and/or ingredient(s) even inmajor amounts. The phrases consisting of and/or composed of close therecited method, apparatus or composition to the inclusion of procedures,structure(s) and/or ingredient(s) other than those recited except forancillaries, adjuncts and/or impurities ordinarily associated therewith.The recital of “essentially” along with “consisting of” or “composed of”renders the recited method, apparatus and/or composition open only forthe inclusion of unspecified procedure(s), structure(s) and/oringredient(s) which do not materially affect the basic novelcharacteristics of the composition. The term coupled, as used herein, isdefined as connected, although not necessarily directly, and notnecessarily mechanically. The term approximately, as used herein, isdefined as at least close to a given value (e.g., preferably within 10%of, more preferably within 1% of, and most preferably within 0.1% of).The term substantially, as used herein, is defined as largely but notnecessarily wholly that which is specified. The term generally, as usedherein, is defined as at least approaching a given state. The termdeploying, as used herein, is defined as designing, building, shipping,installing and/or operating. The term means, as used herein, is definedas hardware, firmware and/or software for achieving a result. The termprogram or phrase computer program, as used herein, is defined as asequence of instructions designed for execution on a computer system. Aprogram, or computer program, may include a subroutine, a function, aprocedure, an object method, an object implementation, an executableapplication, an applet, a servlet, a source code, an object code, ashared library/dynamic load library and/or other sequence ofinstructions designed for execution on a computer or computer system.

All the disclosed embodiments of the invention disclosed herein can bemade and used without undue experimentation in light of the disclosure.The invention is not limited by theoretical statements recited herein.Although the best mode of carrying out the invention contemplated by theinventor(s) is disclosed, practice of the invention is not limitedthereto. Accordingly, it will be appreciated by those skilled in the artthat the invention may be practiced otherwise than as specificallydescribed herein.

It will be manifest that various substitutions, modifications, additionsand/or rearrangements of the features of the invention may be madewithout deviating from the spirit and/or scope of the underlyinginventive concept. It is deemed that the spirit and/or scope of theunderlying inventive concept as defined by the appended claims and theirequivalents cover all such substitutions, modifications, additionsand/or rearrangements.

All the disclosed elements and features of each disclosed embodiment canbe combined with, or substituted for, the disclosed elements andfeatures of every other disclosed embodiment except where such elementsor features are mutually exclusive. Variation may be made in the stepsor in the sequence of steps composing methods described herein.

Although the optical interconnect described herein can be a separatemodule, it will be manifest that the optical interconnect may beintegrated into the system with which it is associated. For instance,the optical backplane may be part of a computer or network. Theindividual components need not be formed in the disclosed shapes, orcombined in the disclosed configurations, but could be provided invirtually any shapes, and/or combined in virtually all configurations.

The appended claims are not to be interpreted as includingmeans-plus-function limitations, unless such a limitation is explicitlyrecited in a given claim using the phrase(s) “means for” and/or “stepfor.” Subgeneric embodiments of the invention are delineated by theappended independent claims and their equivalents. Specific embodimentsof the invention are differentiated by the appended dependent claims andtheir equivalents.

1. An apparatus, comprising a broadcast optical interconnect including:a plurality of nodes positioned to define a node array, each of theplurality of nodes having at least one optical signal emitter and aplurality of optical signal receivers, the plurality of optical signalreceivers positioned to define an individual receiver array that withregard to image forming geometry substantially corresponds to the nodearray; and a plurality of optics optically coupled to the array ofnodes, the plurality of optics positioned to define an optics arraywhose members with regard to image forming geometry substantiallycorrespond to the nodes of the node array and, each of the plurality ofoptics including at least one optical distributing element and anoptical collecting element, wherein diverging elements of the opticsarray with regard to image forming geometry substantially correspond tothe optical receivers of each node of the node array, wherein an opticalsignal from the optical signal emitter is fanned-out by the at least oneoptical distributing element of one of the optics and broadcast to oneof the plurality of receivers of all of the plurality of nodes by theoptical collecting element of all of the plurality of optics.
 2. Theapparatus of claim 1, wherein the at least one optical distributingelement includes a wedge.
 3. The apparatus of claim 1, wherein the atleast one optical distributing element includes a diverging lens.
 4. Theapparatus of claim 1, wherein the at least one optical distributingelement includes a faceted lens having a plurality of facets, one facetfor each optical collecting element.
 5. The apparatus of claim 4,wherein the plurality of facets include a plurality of anamorphicfacets.
 6. The apparatus of claim 1, wherein each optical collectingelement of all of the plurality of optics includes a compound collectinglens.
 7. The apparatus of claim 6, wherein the compound collecting lensincludes two Fresnel lenses.
 8. The apparatus of claim 6, wherein thesplit collecting lens includes two Fresnel lenses.
 9. The apparatus ofclaim 1, wherein each optical collecting element of all of the pluralityof optics includes a split collecting lens.
 10. A method, comprisingoperating a broadcast optical interconnect including: fanning-out anoptical signal from an optical signal emitter, of one of a plurality ofnodes, with an optical distributing element of one of a plurality ofoptics; and substantially simultaneously broadcasting the optical signalto one of a plurality of receivers of all of the plurality of nodes withan optical collecting element of all of the plurality of optics, whereinthe plurality of optics are positioned to define an optics array, theplurality of receivers are positioned to define a receiver array thatcorresponds to the optics array and the plurality of nodes arepositioned to define a node array that substantially corresponds to thereceiver array and the optics array.
 11. The method of claim 10, whereinfanning-out includes refracting the optical signal through a wedge. 12.The method of claim 10, wherein fanning-out includes refracting theoptical signal through a diverging lens.
 13. The method of claim 10,wherein fanning-out includes refracting the optical signal through afaceted lens having a plurality of facets, one facet for each node. 14.The method of claim 13, wherein refracting the optical signal includesconveying the optical signal through a plurality of anamorphic facets.15. The method of claim 10, wherein substantially simultaneousbroadcasting including magnifying.
 16. The method of claim 15, whereinmagnifying includes refracting the optical signal through a compoundcollecting lens.
 17. The method of claim 16, wherein refracting theoptical signal including conveying the optical signal through twoFresnel lenses.
 18. The method of claim 15, wherein magnifying includesrefracting the optical signal through a split collecting lens.